A fuel cell system with a low-temperature cold start function

Abstract

The present invention discloses a fuel cell system with a low-temperature cold start function. Through the setting of a three-way valve, during low-temperature cold start, the hot air coming out of the air compressor directly bypasses the intercooler, preventing the temperature of the hot air from dropping too much after passing through the intercooler. At the same time, through the setting of a bypass air path, when the temperature at the outlet of the air compressor is suitable, the flow rate and pressure at the outlet of the air compressor are both greater than the requirements of the working condition. The excess flow rate directly reaches the tail exhaust air path through the bypass air path without passing through the fuel cell stack. Thus, without the need to reduce the opening degree of the back pressure valve, the air flow rate at the inlet of the fuel cell stack can meet the requirements of the working condition, ensuring that the air compressor does not operate in the surge zone and avoiding violent fluctuations in the flow rate and pressure of the air compressor.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cell technology, and particularly relates to a fuel cell system with a low-temperature cold start function. Background Art

[0002] The fuel cell system will encounter difficulties in starting due to problems such as icing under low-temperature conditions and cannot quickly reach the normal working state.

[0003] When the fuel cell system performs a low-temperature cold start, generally, the heated coolant is passed through the intercooler to heat the air. Among them, using the intercooler to heat the air requires waiting until the coolant temperature is above 0 °C, resulting in a long heating time. Moreover, the intercooler is a fully metal component, with a large amount of external heat exchange and low energy utilization rate. In addition, after the cold start of the stack fails, the temperature of the air used for purging is below zero, and there is a risk of water icing in the membrane electrode.

[0004] For example, the invention patent application with the publication number CN112582649A discloses a stack heating device and a hierarchical control method for a fuel cell system. A preheating valve is added to the air circuit. The inlet pipe of the preheating valve is connected to the second outlet pipe of the intercooler, and the outlet pipe is connected to the air inlet pipe of the air compressor. By using the preheating valve to adjust the air circulation at the outlet of the air compressor and enter the air compressor for heating. However, in a low-temperature environment, since the gas at the rear end of the intercooler needs to be used to heat the inlet air, it is still necessary to wait until the outlet temperature of the intercooler > 0 °C (the air temperature at the outlet and inlet of the intercooler is basically the same in a low-temperature environment), and this time is also relatively long. The air coming out of the air compressor is hot air, and the intercooler will cool the hot air coming out of the air compressor. Therefore, in a low-temperature environment, the air temperature increased by the air compressor will be cooled again after passing through the intercooler.

[0005] The invention application with the publication number CN113299949A discloses a fuel cell thermal management system with a low-temperature cold start function and a control method. Among them, although a three-way valve is added in front of the intercooler, it does not consider that during the startup stage of the system, the load current is small and the required air flow is small. However, to achieve an air compressor outlet temperature > 0 °C or raise it to a suitable working temperature for the stack, it is necessary to increase the rotational speed and outlet pressure of the air compressor. However, in the case of high pressure ratio and low flow, it is very easy to cause the air compressor to surge, or in an environment below -30 °C, the outlet temperature of the air compressor cannot reach the target value. Summary of the Invention

[0006] Aiming at the problem of the slow start rate of the fuel cell stack under low-temperature cold start conditions in the prior art, the present invention provides a fuel cell system with a low-temperature cold start function and a low-temperature cold start control method

[0007] A fuel cell system with a low-temperature cold start function, comprising a fuel cell stack, an air inlet gas path for supplying air to the fuel cell stack, and a tail exhaust air gas path for exhausting the remaining air from the tail of the fuel cell stack. The air inlet gas path has an air compressor, and an intercooler is further provided downstream of the air compressor. A three-way valve is also provided on the air inlet gas path between the air compressor and the intercooler. Two of the interfaces of the three-way valve are respectively used to communicate with the outlet of the air compressor and the inlet of the intercooler, and the third interface of the three-way valve is used to communicate with the outlet of the intercooler.

[0008] A pressure regulating valve for adjusting the air flow rate entering the fuel cell stack is further provided on the air inlet gas path downstream of the intercooler. A bypass gas path with one end communicating with the air inlet gas path and the other end communicating with the tail exhaust air gas path is further provided on the air inlet gas path between the intercooler and the pressure regulating valve. A bypass valve for adjusting the air flow rate entering the tail exhaust air gas path through the bypass gas path is provided on the bypass gas path.

[0009] A back pressure valve is provided on the tail exhaust air gas path, and the bypass gas path communicates with the side of the tail exhaust air gas path downstream of the back pressure valve.

[0010] Preferably, a first air flow meter is provided at the upstream end of the bypass valve on the bypass gas path. The first air flow meter is used to monitor the gas flow rate of the bypass gas path in real time.

[0011] Preferably, a pressure sensor for detecting the air pressure of the air entering the fuel cell stack and a temperature sensor for detecting the air temperature of the air entering the fuel cell stack are provided downstream of the pressure regulating valve on the air inlet gas path.

[0012] Preferably, the fuel cell stack has a box purge inlet. A box purge gas path is connected to a section of the air inlet gas path between the bypass gas path and the pressure regulating valve. The other end of the box purge gas path is connected to the box purge inlet of the fuel cell stack. The box purge pipeline is used to purge the stack. The box purge gas path is a normally open pipeline. During low-temperature cold start, hot air is transmitted to the stack housing and the core. Since the box purge flow rate only accounts for about 1.5% of the air flow rate into the stack, it cannot play a role in regulating the flow rate.

[0013] Preferably, a second air flow meter is further provided upstream of the air compressor on the air inlet gas path, and an air filter is further provided upstream of the second air flow meter. The second air flow meter is used to monitor the air flow rate entering the air compressor in real time. The air filter is used to filter the air entering the air compressor to ensure that the entering air remains clean.

[0014] The present invention further provides a low-temperature cold start control method for the fuel cell system, comprising the following steps:

[0015] (1) Set the initial opening degrees of the three-way valve, pressure regulating valve, back pressure valve, and bypass valve;

[0016] (2) Gradually increase the speed of the air compressor until the set maximum value. During the process of increasing the speed of the air compressor, detect whether the pressure entering the fuel cell stack through the air circuit exceeds the limit value. If it exceeds the limit value, reduce the speed of the air compressor by one gear and gradually increase the opening degree of the back pressure valve until the pressure entering the fuel cell stack through the air circuit does not exceed the limit value; otherwise, proceed to the next step;

[0017] (3) Detect whether the temperature entering the fuel cell stack through the air circuit exceeds the limit value. If it exceeds the limit value, reduce the speed of the air compressor by one gear and gradually increase the opening degree of the three-way valve until the set maximum opening degree; otherwise, proceed to the next step;

[0018] (4) Detect whether the flow rate entering the fuel cell stack through the air circuit exceeds the limit value. If it does not reach the limit value, increase the speed of the air compressor until the set maximum value; if it exceeds the limit value, proceed to the next step;

[0019] (5) Detect whether the speed of the air compressor reaches the set value. If it does not reach, increase the speed of the air compressor until the set maximum value; if it reaches the set value, proceed to the next step;

[0020] (6) Detect whether the flow rate entering the fuel cell stack through the air circuit is greater than the set value. If it is greater than the set value, gradually open the bypass valve until the deviation between the flow rate and the set value is less than 3%; if it is less than the set value, gradually close the bypass valve until the deviation between the flow rate and the set value is less than 3%;

[0021] Detect whether the pressure entering the fuel cell stack through the air circuit is less than the set value. If it is less than the set value, gradually open the pressure regulating valve until the pressure reaches the set value;

[0022] Detect whether the temperature entering the fuel cell stack through the air circuit is less than the set value. If it is less than the set value, gradually open the three-way valve until the opening degree reaches the set maximum opening degree.

[0023] Preferably, the ambient temperature during low-temperature cold start is not lower than -30°C.

[0024] Preferably, in step (1), the initial opening degree of the three-way valve is 70%, the initial opening degree of the pressure regulating valve is 20%, the initial opening degree of the back pressure valve is 52%, and the initial opening degree of the bypass valve is 60%.

[0025] In steps (3) and (6), the set maximum opening degree of the three-way valve is 90%.

[0026] Preferably, the initial value of the speed of the air compressor is 20000 rpm, the set maximum value of the speed of the air compressor is 85000 rpm, and the speed of the air compressor increases by 5000 rpm each time during the increase;

[0027] In step (3), the temperature limit for the air inlet to the fuel cell stack is 80°C.

[0028] In step (6), the set temperature for the air inlet to the fuel cell stack is 70°C.

[0029] Preferably, in step (2), the pressure limit for the air inlet to the fuel cell stack is 2.5 bar.

[0030] In step (6), the set pressure for the air inlet to the fuel cell stack is 2.3 bar.

[0031] In steps (4) and (6), the flow limit or set value for the air inlet to the fuel cell stack is 40% of the rated flow.

[0032] Advantages of the present invention:

[0033] With the present invention, through the setting of the three-way valve, during low-temperature cold start, the hot air from the air compressor directly bypasses the intercooler, preventing excessive temperature drop of the hot air after passing through the intercooler. At the same time, with the present invention, through the setting of the bypass air path, when the temperature at the outlet of the air compressor is suitable, both the flow rate and pressure at the outlet of the air compressor are greater than the operating requirements. The excess flow directly reaches the tail exhaust air path through the bypass air path without passing through the fuel cell stack. Thus, without the need to reduce the opening of the back pressure valve, the air flow rate at the inlet of the fuel cell stack can meet the operating requirements, ensuring that the air compressor does not operate in the surge zone and avoiding drastic fluctuations in the air flow rate and pressure of the air compressor. Description of the Drawings

[0034] Figure 1 It is a schematic structural diagram of a fuel cell system with a low-temperature cold start function according to the present invention.

[0035] Figure 2 It is a flowchart of the low-temperature cold start control method for the fuel cell system according to the present invention. Detailed Embodiments

[0036] Embodiment 1

[0037] As Figure 1 shown is a schematic structural diagram of a fuel cell system with a low-temperature cold start function according to the present invention. The fuel cell system with a low-temperature cold start function according to the present invention includes a fuel cell stack 1, an air inlet path 2 for supplying air to the fuel cell stack 1, and a tail exhaust air path 3 for exhausting the remaining air from the fuel cell stack 1. Since the fuel cell system in this application does not involve improvements in the hydrogen inlet and outlet gas paths and the cooling system structure, these structures are not shown in the figure and will not be elaborated here.

[0038] The air intake air path 2 is equipped with an air compressor 21. Downstream of the air compressor 21 (the upstream and downstream are divided according to the gas flow direction), an intercooler 22 is also provided. A three-way valve 23 is further provided on the air intake air path 2 between the air compressor 21 and the intercooler 22. Two of the interfaces of the three-way valve 23 are respectively used to communicate with the outlet of the air compressor 21 and the inlet of the intercooler 22, and the third interface of the three-way valve 23 is used to communicate with the outlet of the intercooler 22. That is to say, two of the interfaces of the three-way valve 23 respectively communicate with the inlet and outlet of the intercooler 22, so that the air flow can directly bypass the intercooler 22 and enter the fuel cell stack 1 when needed, avoiding the higher-temperature air coming out of the air compressor 21 being cooled after passing through the intercooler 22 during low-temperature startup.

[0039] A pressure regulating valve 24 for adjusting the air flow rate entering the fuel cell stack 1 is further provided on the air intake air path 2 downstream of the intercooler 22. A bypass air path 4 with one end communicating with the air intake air path 2 and the other end communicating with the tail exhaust air path 3 is also provided on the air intake air path 2 between the intercooler 22 and the pressure regulating valve 24. A bypass valve 41 for adjusting the air flow rate entering the tail exhaust air path 3 through the bypass air path 4 is provided on the bypass air path 4. A back pressure valve 31 is provided on the tail exhaust air path 3, and the bypass air path 4 communicates with the side of the tail exhaust air path 3 downstream of the back pressure valve 31. That is to say, during low-temperature cold startup, the relatively high-temperature air flow coming out of the air compressor 21 directly reaches the fuel cell stack 1 through the three-way valve 23, and the pressure regulating valve 24 controls the air flow rate entering the fuel cell stack 1, and the excess air directly enters the tail exhaust air path 3 through the bypass air path 4 for tail exhaust. A first air flow meter 42 is provided at the upstream end of the bypass air path 4 upstream of the bypass valve 41, and the gas flow rate entering the bypass air path 4 is monitored in real time through the first air flow meter 42.

[0040] A pressure sensor 25 for detecting the air pressure of the air entering the fuel cell stack 1 and a temperature sensor 26 for detecting the air temperature of the air entering the fuel cell stack 1 are provided on the air intake air path 2 downstream of the pressure regulating valve 24. A second air flow meter 27 is also provided on the air intake air path 2 upstream of the air compressor 21, and an air filter 28 is provided upstream of the second air flow meter 27. The air filter 28 is used to filter the air entering the air compressor 21 to ensure clean air.

[0041] The fuel cell stack 1 also has a box purge inlet. A box purge air path 5 is connected to a section of the air intake air path 2 between the bypass air path 4 and the pressure regulating valve 24. The other end of the box purge air path 5 is connected to the box purge inlet of the fuel cell stack 1. The box purge air path 5 is used to purge the stack. The box purge air path 5 is a normally open pipeline. During low-temperature cold startup, hot air is transferred to the stack housing and the stack core. Since the box purge flow rate only accounts for about 1.5% of the air flow rate into the stack, it cannot play a role in regulating the flow rate.

[0042] With the setting of the three-way valve 23 in the present invention, during low-temperature cold start, the hot air coming out of the air compressor 21 directly bypasses the intercooler 22, avoiding excessive temperature reduction of the hot air after passing through the intercooler 22. At the same time, with the setting of the bypass air passage 4 in the present invention, when the outlet temperature of the air compressor 21 is suitable, the outlet flow rate and pressure of the air compressor 21 are both greater than the operating conditions requirements. The excess flow rate directly goes to the tail exhaust air passage through the bypass air passage 4 without passing through the fuel cell stack. Thus, without the need to reduce the opening degree of the back pressure valve 31, the air flow rate at the inlet of the fuel cell stack can meet the operating conditions requirements, ensuring that the air compressor 21 does not operate in the surge zone and avoiding drastic fluctuations in the flow rate and pressure of the air compressor 21.

[0043] Embodiment 2

[0044] When the ambient temperature of the fuel cell system is -30°C, the low-temperature cold start of the fuel cell system is achieved through the following scheme.

[0045] The flowmeter at the rear end of the air filter 28 (the second air flowmeter 27) monitors the flow rate as the inlet flow rate of the air compressor 21, with the parameter value being Q1. The flowmeter at the inlet of the bypass valve 41 (the first air flowmeter 42) monitors the bypass flow rate, with the parameter value being Q2. Then the air flow rate into the fuel cell stack is Q1 - Q2, which is Q3.

[0046] To make the inlet temperature of the fuel cell air system meet the requirements for entering the fuel cell stack, during the system self-check process, the opening degree of the three-way valve 23 should be adjusted to the heating circuit, the pressure regulating valve 24 should be closed, the opening degree of the bypass valve 41 should be 50%, and the back pressure valve 31 should be closed.

[0047] During the system operation stage, the hydrogen inlet pressure follows the air inlet pressure. The specific adjustment process is as follows:

[0048] (1) Set the initial opening degrees of the three-way valve, pressure regulating valve, back pressure valve, and bypass valve.

[0049] The initial opening degree of the three-way valve is 70%, the initial opening degree of the pressure regulating valve is 20%, the initial opening degree of the back pressure valve is 52%, and the initial opening degree of the bypass valve is 60%. The initial value of the air compressor speed is 20000 rpm, the maximum value set for the air compressor speed is 85000 rpm, and each time the air compressor speed increases, it increases by 5000 rpm.

[0050] (2) Gradually increase the air compressor speed until the set maximum value. During the process of increasing the air compressor speed, detect whether the pressure entering the fuel cell stack in the air passage exceeds the limit value. The pressure limit value for the air passage entering the fuel cell stack is 2.5 bar. If it exceeds the limit value, reduce one gear of the air compressor speed and gradually increase the opening degree of the back pressure valve until the pressure entering the fuel cell stack in the air passage does not exceed the limit value; otherwise, proceed to the next step;

[0051] (3) Detect whether the temperature of the air flow path entering the fuel cell stack exceeds the limit value. The temperature limit value of the air flow path entering the fuel cell stack is 80 °C. If it exceeds the limit value, reduce the air compressor speed by one gear and gradually increase the opening degree of the three-way valve until the set maximum opening degree; otherwise, proceed to the next step. In steps (3) and (6), the maximum opening degree set for the three-way valve is 90%.

[0052] (4) Detect whether the flow rate of the air flow path entering the fuel cell stack exceeds the limit value. The flow rate limit value of the air flow path entering the fuel cell stack is 40% of the rated flow rate. If it does not reach the limit value, increase the air compressor speed until the set maximum value; if it exceeds the limit value, proceed to the next step;

[0053] (5) Detect whether the air compressor speed reaches the set value. If it does not reach, increase the air compressor speed until the set maximum value; if it reaches the set value, proceed to the next step;

[0054] (6) Detect whether the flow rate of the air flow path entering the fuel cell stack is greater than the set value. The set value of the flow rate of the air flow path entering the fuel cell stack is 40% of the rated flow rate. If it is greater than the set value, gradually open the bypass valve until the deviation between the flow rate and the set value is less than 3%; if it is less than the set value, gradually close the bypass valve until the deviation between the flow rate and the set value is less than 3%;

[0055] Detect whether the pressure of the air flow path entering the fuel cell stack is less than the set value. The set value of the pressure of the air flow path entering the fuel cell stack is 2.3 bar. If it is less than the set value, gradually open the pressure regulating valve until the pressure reaches the set value;

[0056] Detect whether the temperature of the air flow path entering the fuel cell stack is less than the set value. The set value of the temperature of the air flow path entering the fuel cell stack is 70 °C. If it is less than the set value, gradually open the three-way valve until the opening degree reaches the set maximum opening degree. The maximum opening degree set for the three-way valve is 90%.

Claims

1. A low-temperature cold start control method for a fuel cell system, characterized in that, the fuel cell system includes a fuel cell stack, an air inlet air path for supplying air to the fuel cell stack, and a tail exhaust air path for exhausting the remaining air from the tail of the fuel cell stack. The air inlet air path has an air compressor, and an intercooler is further provided downstream of the air compressor. A three-way valve is also provided on the air inlet air path between the air compressor and the intercooler. Two of the interfaces of the three-way valve are respectively used to communicate with the outlet of the air compressor and the inlet of the intercooler, and the third interface of the three-way valve is used to communicate with the outlet of the intercooler. A pressure regulating valve for adjusting the air flow rate entering the fuel cell stack is further provided downstream of the intercooler on the air inlet air path. A bypass air path with one end communicating with the air inlet air path and the other end communicating with the tail exhaust air path is also provided between the intercooler and the pressure regulating valve on the air inlet air path. A bypass valve for adjusting the air flow rate entering the tail exhaust air path through the bypass air path is provided on the bypass air path. A back pressure valve is provided on the tail exhaust air path, and the bypass air path communicates with the side of the tail exhaust air path downstream of the back pressure valve. The ambient temperature during low-temperature cold start is not lower than -30°C. The low-temperature cold start control method includes the following steps: (1) Set the initial opening degrees of the three-way valve, the pressure regulating valve, the back pressure valve, and the bypass valve. (2) Gradually increase the speed of the air compressor until the set maximum value. During the process of increasing the speed of the air compressor, detect whether the pressure of the air entering the fuel cell stack through the air path exceeds the limit value. If it exceeds the limit value, reduce the speed of the air compressor by one gear and gradually increase the opening degree of the back pressure valve until the pressure of the air entering the fuel cell stack through the air path does not exceed the limit value; otherwise, proceed to the next step. (3) Detect whether the temperature of the air entering the fuel cell stack through the air path exceeds the limit value. If it exceeds the limit value, reduce the speed of the air compressor by one gear and gradually increase the opening degree of the three-way valve until the set maximum opening degree; otherwise, proceed to the next step. (4) Detect whether the flow rate of the air entering the fuel cell stack through the air path exceeds the limit value. If it does not reach the limit value, increase the speed of the air compressor until the set maximum value; if it exceeds the limit value, proceed to the next step. (5) Detect whether the speed of the air compressor reaches the set value. If it does not reach, increase the speed of the air compressor until the set maximum value; if it reaches the set value, proceed to the next step. (6) Detect whether the flow rate of the air entering the fuel cell stack through the air path is greater than the set value. If it is greater than the set value, gradually open the bypass valve until the deviation between the flow rate and the set value is less than 3%; if it is less than the set value, gradually close the bypass valve until the deviation between the flow rate and the set value is less than 3%. Detect whether the pressure of the air entering the fuel cell stack through the air path is less than the set value. If it is less than the set value, gradually open the pressure regulating valve until the pressure reaches the set value. Detect whether the temperature of the air entering the fuel cell stack through the air path is less than the set value. If it is less than the set value, gradually open the three-way valve until the opening degree reaches the set maximum opening degree.

2. The low-temperature cold start control method for a fuel cell system according to claim 1, characterized in that, In step (1), the initial opening degree of the three-way valve is 70%, the initial opening degree of the pressure regulating valve is 20%, the initial opening degree of the back pressure valve is 52%, and the initial opening degree of the bypass valve is 60%. In steps (3) and (6), the maximum opening degree set for the three-way valve is 90%.

3. The low-temperature cold start control method of the fuel cell system according to claim 1, characterized in that, the initial value of the air compressor speed is 20,000 rpm, the maximum value set for the air compressor speed is 85,000 rpm, and it increases by 5,000 rpm each time when the air compressor speed rises; in step (3), the temperature limit value of the air entering the fuel cell stack through the air path is 80 °C; in step (6), the temperature set value of the air entering the fuel cell stack through the air path is 70 °C.

4. The low-temperature cold start control method of the fuel cell system according to claim 1, characterized in that, in step (2), the pressure limit value of the air entering the fuel cell stack through the air path is 2.5 bar; in step (6), the pressure set value of the air entering the fuel cell stack through the air path is 2.3 bar; in steps (4) and (6), the flow limit value or set value of the air entering the fuel cell stack through the air path is 40% of the rated flow.

5. The low-temperature cold start control method of the fuel cell system according to claim 1, characterized in that, a first air flow meter is provided at the upstream end of the bypass valve on the bypass air path.

6. The low-temperature cold start control method of the fuel cell system according to claim 1, characterized in that, a pressure sensor for detecting the air pressure entering the fuel cell stack and a temperature sensor for detecting the air temperature entering the fuel cell stack are provided downstream of the pressure regulating valve on the air inlet air path.

7. The low-temperature cold start control method of the fuel cell system according to claim 1, characterized in that, the fuel cell stack has a box purging inlet, and a box purging air path is connected to a section of the air inlet air path between the bypass air path and the pressure regulating valve, and the other end of the box purging air path is connected to the box purging inlet of the fuel cell stack.

8. The low-temperature cold start control method of the fuel cell system according to claim 1, characterized in that, a second air flow meter is further provided upstream of the air compressor on the air inlet air path, and an air filter is further provided upstream of the second air flow meter.

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