Flow and pressure collaborative control method in hydrogen fuel cell durability evaluation

Abstract

The application relates to a hydrogen fuel cell durability evaluation flow and pressure cooperative control method, which comprises the following steps: calculating the required hydrogen and air flow of a fuel cell according to hydrogen fuel cell durability working condition information; adopting an intermediate buffer point set value control mode in a large variable load loading process to obtain multiple flow and pressure step set points; installing a fuel cell stack connected with a fuel cell test table and starting the fuel cell test table; selecting a flow mode for the fuel cell test table air supply mode, setting a flow value first and then setting a pressure value as a one-step mode to load; circulating each step to complete the large variable load loading process. Compared with the prior art, the pressure fluctuation in the large variable load process is minimized, the situation that the pressure difference between the two sides of a membrane electrode caused by the pressure fluctuation of the fuel cell is too large is effectively solved, the damage of the membrane electrode caused by the durability test is reduced, and the service life of the fuel cell is improved.

Description

Technical Field

[0001] This invention relates to the field of hydrogen fuel cell technology, and in particular to a method for the coordinated control of flow rate and pressure in the durability evaluation of hydrogen fuel cells. Background Technology

[0002] With increasingly stringent environmental regulations and the depletion of fossil fuels, hydrogen energy is receiving growing attention worldwide. Hydrogen fuel cells, also known as proton exchange membrane fuel cells (PEMFCs), are advanced energy conversion devices that use hydrogen as fuel. They offer advantages such as high efficiency, cleanliness, and long driving range. Their low operating temperature and rapid start-up capability at low temperatures make them currently the most suitable fuel cells for vehicle engines. To develop high-performance, low-cost, and long-life fuel cell products and promote their commercial application, fuel cell durability is receiving increasing attention from the industry.

[0003] During vehicle operation, frequent changes in operating conditions are the primary cause of reduced fuel cell lifespan. Transient changes in current load cause frequent fluctuations in reactant gas pressure, flow rate, temperature, and humidity, leading to mechanical damage to the materials themselves or component structures. Specifically, at the moment of loading, the flow rate response lags behind the loading electrical signal, causing a short-term fuel starvation phenomenon. This instantaneous fuel starvation increases the anode potential, leading to carbon oxidation. Furthermore, pressure fluctuations result in poor consistency across individual fuel cell units. In actual testing, changes in load and flow rate also cause pressure fluctuations in the back pressure membrane, causing the stack inlet pressure to operate within an unstable range, thus affecting fuel cell performance.

[0004] Current technologies for controlling large-load variations in durability testing typically employ a metering ratio mode. This mode can lead to insufficient gas supply, resulting in fuel cell stack "starvation," which reduces stack output power and may even cause proton exchange membrane burnout. While a "feedforward" control strategy, which pre-loads a certain amount of reactant gas before loading, can mitigate the "gas shortage" phenomenon to some extent, under large-load variations, a sudden increase in current can cause a sudden increase in flow rate, leading to pressure fluctuations. (See [link to relevant documentation]). Figure 2 This can cause excessive pressure difference between the inlet and outlet of the fuel cell stack, damaging the membrane electrode assembly and reducing the performance of the fuel cell.

[0005] The patent with publication number CN111106366A discloses a fuel cell stack test bench for testing fuel cell performance. The test bench adjusts the back pressure in real time and quickly by adding a back pressure control module. The design is complex and costly, and it can only control pressure fluctuations individually, and cannot achieve coordinated control of flow and pressure. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by providing a method for coordinated control of flow and pressure in the durability evaluation of hydrogen fuel cells. This method addresses the issue of excessive pressure difference across the membrane electrode assembly caused by pressure fluctuations, reduces damage to the membrane electrode assembly during durability testing, and improves the lifespan of the fuel cell.

[0007] Therefore, the applicant believes that effectively controlling the pressure and flow rate of the gas supply system is the key to improving the efficiency and reliability of fuel cells. Designing an effective control strategy for the gas supply system to enable the gas supply to respond quickly to the load power request and maintain the stable pressure of the reactant gas in the stack is of great significance for improving the efficiency of fuel cells and extending their service life.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] This invention provides a method for the coordinated control of flow rate and pressure in the durability evaluation of hydrogen fuel cells, comprising the following steps:

[0010] S001: Calculate the required flow rates of hydrogen and air for the fuel cell based on the endurance operating condition information of the hydrogen fuel cell;

[0011] S002: By adopting a control method of adding intermediate buffer point setpoints during the large load change process, multiple step-by-step setpoints for flow rate and pressure are obtained;

[0012] S003: Install and connect the fuel cell stack to the fuel cell test bench, and start the fuel cell test bench;

[0013] S004: Select the flow mode for the gas supply method of the fuel cell test bench, and load it in one step by first setting the flow value and then setting the pressure value to obtain the change data of the inlet and outlet pressure of the anode and cathode.

[0014] S005: Based on the multiple step-by-step setpoints obtained in S002, each step is performed cyclically to complete the large load change process.

[0015] Furthermore, in S001, the operating condition information includes the current increase range and the anode and cathode pressure increase range.

[0016] Furthermore, in S001, the starting values ​​of hydrogen and air flow rates are calculated based on the starting value of the current increase range.

[0017] Furthermore, in S001, the endpoint values ​​of hydrogen and air flow rates are calculated based on the endpoint values ​​of the current amplification range.

[0018] Furthermore, in S001, the required hydrogen flow rate is calculated as follows:

[0019]

[0020] Furthermore, in S001, the required airflow is calculated as follows:

[0021]

[0022] In the formula: F H2 and F Air These represent the flow rates of hydrogen and air, respectively, with St being the metering ratio;

[0023] 22.42 is the volume of 1 mol of hydrogen gas under standard conditions;

[0024] 60 seconds is the unit of conversion to 1 minute;

[0025] 96485C is the amount of charge carried by one mole of electrons;

[0026] In equation (1), 2 represents the number of electrons transferred in 1 mole of hydrogen gas;

[0027] In equation (2), 4 represents the number of electrons transferred in 1 mole of oxygen, and 0.21 represents the oxygen content in the air.

[0028] Furthermore, in S002, it is first determined whether the loading rate meets the large load variation condition, and then a control method of adding intermediate buffer point setting value is adopted.

[0029] Furthermore, in S002, based on the process of increasing buffer points during large load changes, intermediate hydrogen flow buffer points, intermediate air flow buffer points, intermediate anode pressure buffer points, and intermediate cathode pressure buffer points are uniformly set.

[0030] Furthermore, in S002, the step size of the intermediate hydrogen flow buffer point is 5 to 18 NLPM, and the step size of the intermediate air flow buffer point is 15 to 25 NLPM.

[0031] Furthermore, in S002, the step size of the anode and cathode pressure buffer points is 10-30 kPa.

[0032] Compared with the prior art, the present invention has the following technical advantages:

[0033] 1) This method uses a flow mode during the test, which avoids the pressure fluctuation caused by a sudden increase in flow rate in a short period of time due to a sudden increase in current in the metering ratio mode;

[0034] 2) This method reduces the damage to the membrane electrode during durability testing. Pressure fluctuations can easily cause a large pressure difference between the anode and cathode of the fuel cell stack, which can have a certain negative impact on the mechanical strength of the membrane electrode.

[0035] 3) This method improves the durability of the fuel cell stack. In flow mode, the test platform responds to the set gas flow rate first, and then changes the current density to avoid gas shortage when the current density increases. In metering mode, the test platform responds to the change in current density first, and then to the change in flow rate, which poses a risk of gas shortage in the stack and reduces the durability of the fuel cell stack. Attached Figure Description

[0036] Figure 1 A flowchart of the flow and pressure control method of the present invention is shown.

[0037] Figure 2 A pressure data graph of the prior art control method is shown.

[0038] Figure 3 A pressure data graph of the control method of the present invention is shown. Detailed Implementation

[0039] This invention discloses a method for coordinated control of flow rate and pressure during fuel cell stack durability testing. The method primarily involves determining the required flow rate at various current points after defining the hydrogen fuel cell durability test conditions. Then, during the test, a "set flow rate → adjust pressure → apply large load variations" approach is used to ensure stable changes in flow rate and pressure throughout the test. Compared to existing technologies, this invention uses a flow rate mode instead of a metering ratio mode, avoiding the stack gas shortage situation caused by the metering ratio mode. It also minimizes pressure fluctuations during large load variations, effectively solving the problem of excessive pressure difference across the membrane electrode assembly (MEA) caused by pressure fluctuations, reducing damage to the MEA during durability testing, and improving the fuel cell's lifespan.

[0040] Specifically, the method for coordinated control of flow rate and pressure in the durability evaluation of hydrogen fuel cells in this invention includes the following steps:

[0041] S001. Calculate the required flow rate of the fuel cell based on the durability operating condition information (as shown below): The flow rate can be calculated based on the ratio of the volume of charge consumed to the total amount of charge transferred by electrons at different operating points during the internal chemical reaction of the fuel cell. The calculation formula is as follows:

[0042]

[0043]

[0044] In the formula: F H2 and F Air These represent the flow rates of hydrogen and air, respectively, with St being the metering ratio;

[0045] 22.42 is the volume of 1 mol of hydrogen gas under standard conditions;

[0046] 60 seconds is the unit of conversion to 1 minute;

[0047] 96485C is the amount of charge carried by one mole of electrons;

[0048] In equation (1), 2 represents the number of electrons transferred in 1 mole of hydrogen gas;

[0049] In equation (2), 4 represents the number of electrons transferred in 1 mole of oxygen, and 0.21 represents the oxygen content in the air.

[0050] S002. During the large load change process, a control method is adopted to add intermediate buffer point settings, and the flow rate and pressure are set in several parts step by step.

[0051] S003. Connect the fuel cell stack to the fuel cell test bench and start the fuel cell test bench.

[0052] S004. Select the flow mode for gas supply and adopt the method of "set flow rate → adjust pressure → variable load loading";

[0053] S005, repeat the process to complete the large load change process.

[0054] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Any structural / module names, control modes, algorithms, processes, or composition ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0055] Example 1

[0056] This embodiment provides a method for the coordinated control of flow rate and pressure during fuel cell stack durability testing. The specific steps are as follows: Figure 1 As shown.

[0057] In this embodiment, the endurance test requires the current of a 15-cell fuel cell stack to increase from 457A to 697A, the anode pressure to increase from 100kPa to 160kPa, and the cathode pressure to increase from 90kPa to 150kPa. Preliminary assessment indicates that this loading rate is suitable for large load variations. An intermediate buffer point can be added to control the flow rate and pressure. This control method includes the following steps:

[0058] (1) Calculate the required flow rate at the operating point according to the formula. The required flow rates of hydrogen and air for 457A are 72 NLPM and 178 NLPM, respectively; the required flow rates of hydrogen and air for 697A are 105 NLPM and 232 NLPM, respectively.

[0059] (2) Calculate the required flow rate for each buffer point. The hydrogen flow rate (unit: NLPM) that can be increased at the buffer points is: 72, 83, 94, 105; the corresponding air flow rate (unit: NLPM) is: 178, 196, 214, 232; the anode pressure buffer point (unit: kPa) can be: 100, 115, 130, 145, 160; the cathode pressure buffer point (unit: kPa) can be: 90, 105, 120, 135, 150;

[0060] (3) Install and connect the fuel cell stack to the fuel cell test bench, check the equipment software and hardware, and start the fuel cell test bench after confirming that there are no errors, and test the stack normally.

[0061] (4) Gas supply method selection: Select flow mode. Based on the above gas flow rate and pressure buffer point, first set the flow rate value, then set the pressure value, and finally apply the load. The anode inlet and outlet pressures are as follows: Figure 3 As shown;

[0062] (5) The process is repeated to complete the large load change process. This avoids the gas shortage phenomenon that occurs when the current density increases. In the metering ratio mode, the test platform will respond to the change in current density first and then the change in flow rate, which poses a risk of gas shortage in the stack and reduces the durability of the fuel cell stack.

[0063] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for coordinated control of flow rate and pressure in the durability evaluation of hydrogen fuel cells, characterized in that, Includes the following steps: S001: Calculate the required flow rates of hydrogen and air for the fuel cell based on the endurance operating condition information of the hydrogen fuel cell; S002: By adopting a control method of adding intermediate buffer point setpoints during the large load change process, multiple step-by-step setpoints for flow rate and pressure are obtained; S003: Install and connect the fuel cell stack to the fuel cell test bench, and start the fuel cell test bench; S004: Select the flow mode for the gas supply method of the fuel cell test bench, and load it in one step by first setting the flow value and then setting the pressure value to obtain the change data of the inlet and outlet pressure of the anode and cathode. S005: Based on the multiple step-by-step setpoints obtained in S002, each step is performed cyclically to complete the large load loading process; In S002, based on the process of increasing buffer points during large load changes, intermediate hydrogen flow buffer points, intermediate air flow buffer points, intermediate anode pressure buffer points, and intermediate cathode pressure buffer points are uniformly set.

2. The method for coordinated control of flow rate and pressure in the durability evaluation of a hydrogen fuel cell according to claim 1, characterized in that, In S001, the operating condition information includes the current increase range and the anode and cathode pressure increase range.

3. The method for coordinated control of flow rate and pressure in the durability evaluation of a hydrogen fuel cell according to claim 1, characterized in that, In S001, the starting values ​​of hydrogen and air flow rates are calculated based on the starting value of the current increase range.

4. The method for coordinated control of flow rate and pressure in the durability evaluation of a hydrogen fuel cell according to claim 1, characterized in that, In S001, the endpoint values ​​of hydrogen and air flow rates are calculated based on the endpoint values ​​of the current amplification range.

5. The method for coordinated control of flow rate and pressure in the durability evaluation of a hydrogen fuel cell according to claim 1, characterized in that, In S001, the required hydrogen flow rate is calculated as follows: （1）。 6. The method for coordinated control of flow rate and pressure in the durability evaluation of a hydrogen fuel cell according to claim 1, characterized in that, In S001, the required airflow is calculated as follows: （2）。 7. The method for coordinated control of flow rate and pressure in the durability evaluation of a hydrogen fuel cell according to claim 1, characterized in that, In S002, it is first determined whether the loading rate meets the large load change condition, and then a control method of adding intermediate buffer point setting value is adopted.

8. The method for coordinated control of flow rate and pressure in the durability evaluation of a hydrogen fuel cell according to claim 1, characterized in that, In S002, the step size of the intermediate hydrogen flow rate buffer point is 5~18 NLPM, and the step size of the intermediate air flow rate buffer point is 15~25 NLPM.

9. The method for coordinated control of flow rate and pressure in the durability evaluation of a hydrogen fuel cell according to claim 1, characterized in that, In S002, the step size of the anode and cathode pressure buffer points is 10~30 kPa.

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