Method for determining a single low form of a fuel cell stack

Abstract

This invention relates to the field of fuel cell stack technology, and specifically discloses a method for determining the voltage of a single cell in a fuel cell stack, comprising: acquiring the voltage of each individual cell in the fuel cell stack; and recording the voltage of the individual cell with the lowest voltage value as the lowest cell voltage. V 0; Calculate the average voltage of a normal cell in the fuel cell stack. V 2. Then calculate the average voltage of a normal battery. V 2 and minimum battery voltage V The difference between 0 and 1; based on the obtained load current density of the fuel cell stack. i The difference is compared with the maximum voltage loss caused by hydrogen permeation. V 1. Compare or compare the difference with the maximum voltage drop caused by mass transfer. V 3. A comparison is made, and based on the comparison results, the single-low configuration of the fuel cell stack is determined, and the corresponding control strategy is output. This invention can quickly locate and analyze the single-low configuration under all operating conditions, provide a precise control strategy, thereby reducing membrane electrode damage and extending stack life.

Description

Technical Field

[0001] This invention relates to the field of fuel cell stack technology, and in particular to a method for determining the single low-temperature form of a fuel cell stack. Background Technology

[0002] A fuel cell stack consists of several individual cell units (membrane electrode assembly + bipolar plate). During the operation of a fuel cell stack, there may be instances where the voltage of a single cell is too low. The reasons for this low voltage include: 1. Material factors: Due to inherent differences between the membrane electrode assemblies, their performance varies under the same tensile load. 2. Mass transfer factors: Differences in manufacturing processes and the hydrophilicity / hydrophobicity of the materials used in the bipolar plates and membrane electrode assemblies result in varying pressure forces on the surface of each membrane electrode assembly during stacking and different degrees of drainage during operation. These variations lead to different mass transfer capabilities and performance, ultimately resulting in a low voltage in a single cell, creating a vicious cycle where the poorest cell continues to deteriorate.

[0003] If the voltage of a single cell in the fuel cell stack is too low, it will not only lead to an excessively large polarity difference in the stack, affecting the normal load-bearing capacity of the stack, but will also create a chain reaction in surrounding cells. Over time, this will cause irreversible damage to the membrane electrode assembly (MEA) and shorten the lifespan of the fuel cell stack. In severe cases, it can cause reverse polarity of the MEA in the stack, leading to MEA perforation, hydrogen-oxygen mixing, and other safety accidents.

[0004] Current methods involve changing the operating conditions of the fuel cell stack, such as temperature and humidity, and observing the response changes in the voltage of a single low-voltage section to determine the cause of the low voltage and then providing corresponding strategies. For example, increasing the intake air humidity and observing whether the voltage of the single low-voltage section increases indicates that the membrane in that section is dry, and the solution is to increase the humidity. Similarly, if the voltage of the single low-voltage section does not increase, other operating conditions are changed, and the high-frequency intercept and low-frequency impedance of the EIS testing equipment are used to analyze whether it is due to water flooding or membrane dryness.

[0005] Current technology relies on observing changes in the voltage response of a single low-voltage section by altering the operating conditions of the fuel cell stack to determine the cause of a single low-voltage section. This requires constantly changing operating conditions, which is somewhat haphazard and time-consuming. Sometimes, even after changing all conditions, the single low-voltage remains unchanged, leading to inaccurate judgments. Even with comprehensive analysis using EIS testing equipment, only water flooding and membrane dryness can be identified. However, when the proton exchange membrane is water-saturated, its ohmic impedance remains almost constant, which also affects the judgment, ultimately wasting human, material, and financial resources. Furthermore, the entire analysis process is lengthy, and effective measures cannot be taken promptly to address the observed phenomena, posing certain safety risks.

[0006] During actual operation of the fuel cell stack, due to the inherent characteristics and differences of the materials, the single low-current-density phenomenon manifests in two ways: high hydrogen permeation and low reactant concentration on the catalyst surface (limited mass transfer). However, assuming the membrane electrode assembly (MEA) does not fail, hydrogen permeation primarily affects the low current density range (500 A / cm²). 2 Previously, under medium to high current density, mass transfer was the main factor affecting the performance of the fuel cell stack. Therefore, if the two are distinguished, it is possible to determine and analyze the single low current form of the fuel cell stack, as well as to perform single low current form analysis under all operating conditions, and thus accurately take corresponding strategies. Summary of the Invention

[0007] To address the shortcomings and deficiencies in existing technologies, this invention provides a method for determining the single low-temperature state of a fuel cell stack. This method can quickly locate and analyze the single low-temperature state under all operating conditions, provide a precise control strategy, thereby reducing membrane electrode damage and extending stack life.

[0008] As a first aspect of the present invention, a method for determining the single low-temperature condition of a fuel cell stack is provided, the method comprising:

[0009] Step S1: Obtain the voltage of each individual cell in the fuel cell stack;

[0010] Step S2: Select the single cell with the lowest voltage value and record the voltage value of the single cell with the lowest voltage value as the lowest cell voltage V0;

[0011] Step S3: Calculate the average voltage V2 of the normal cell in the fuel cell stack, and then calculate the difference ΔV between the average voltage V2 of the normal cell and the lowest cell voltage V0.

[0012] Step S4: Obtain the load current density i of the fuel cell stack;

[0013] Step S5: Based on the load current density i of the fuel cell stack, compare the difference ΔV with the maximum voltage loss V1 caused by hydrogen permeation or compare the difference ΔV with the maximum voltage loss V3 caused by mass transfer. Then, determine the single-low form of the fuel cell stack based on the comparison result and output the corresponding control strategy.

[0014] Furthermore, step S5 also includes:

[0015] Determine whether the load current density i of the fuel cell stack is less than a preset value;

[0016] If the load current density i is less than the preset value, the difference ΔV is compared with the maximum voltage loss V1 formed by hydrogen permeation. Then, based on the first comparison result, the single low form of the fuel cell stack is determined, and the corresponding control strategy is output.

[0017] If the load current density i is not less than the preset value, the difference ΔV is compared with the maximum voltage loss V3 formed by the mass transfer. Then, based on the second comparison result, the single low form of the fuel cell stack is determined, and the corresponding control strategy is output.

[0018] Furthermore, the formula for calculating the maximum voltage loss V1 caused by hydrogen permeation is as follows:

[0019]

[0020] Where α is the transfer coefficient, i cross i is the hydrogen permeation current density, and i0 is the exchange current density.

[0021] Furthermore, the formula for calculating the maximum voltage loss V3 caused by the mass transfer is as follows:

[0022]

[0023] Among them, i L Let be the limiting current density, and i be the tensile current density.

[0024] Furthermore, the limiting current density i L The calculation formula is as follows:

[0025]

[0026] Where D represents the diffusion coefficient of the reactant component, C represents the total concentration of the reactant, and δ represents the diffusion distance.

[0027] Furthermore, the formula for calculating the average voltage V2 of a normal cell in the fuel cell stack is as follows:

[0028]

[0029] Where V is the total voltage of the fuel cell stack, N is the number of cells in a single fuel cell stack, and V0 is the lowest cell voltage.

[0030] Furthermore, the formula for calculating the difference ΔV between the average voltage V2 of the normal battery and the lowest battery voltage V0 is as follows:

[0031] ΔV = V2 - V0.

[0032] Furthermore, the step of comparing the difference ΔV with the maximum voltage loss V1 caused by hydrogen permeation, then determining the single-low form of the fuel cell stack based on the first comparison result, and outputting the corresponding control strategy, further includes:

[0033] If ΔV > V1, excessive hydrogen permeation may occur in the single cell with the lowest voltage value at this time, and it is necessary to further judge through the open-circuit voltage or stop the machine;

[0034] If ΔV < V1, mass transfer limitation may occur in the single cell with the lowest voltage value at this time, and it is necessary to increase the intake air flow for purging.

[0035] Further, comparing the difference ΔV with the maximum voltage loss V3 formed by the mass transfer, and then judging the single-low form of the fuel cell stack according to the second comparison result and outputting the corresponding control strategy further includes:

[0036] If ΔV > V3, severe mass transfer limitation may occur in the single cell with the lowest voltage value at this time, and it is necessary to stop the machine immediately;

[0037] If ΔV < V3, it is necessary to change the operating condition of the fuel cell stack. If the single cell with the lowest voltage value improves, it will operate for a period of time under the current operating condition. If the single cell with the lowest voltage value still does not improve, it is necessary to stop the machine for purging.

[0038] Further, the preset value is 500 mA / cm 2 .

[0039] The method for judging the single-low form of the fuel cell stack provided by the present invention has the following advantages: According to the magnitude of the current density and the influence mechanism of the single-low reaction, the entire loading condition is divided into two segments, namely, low current density (less than 500 mA / cm 2 ) and medium-high current density (greater than or equal to 500 mA / cm 2 ). By comparing the difference between the average voltage of the normal cell and the voltage of the lowest cell collected by CVM with the maximum voltage loss generated under different influence mechanisms, it is possible to quickly locate and analyze the single-low form under all operating conditions, give accurate control strategies, thereby reducing the damage of the membrane electrode and extending the life of the stack. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification, and are used together with the following specific embodiments to explain the present invention, but do not constitute a limitation to the present invention.

[0041] Figure 1 It is a flowchart of the method for judging the single-low form of the fuel cell stack provided by the present invention.

[0042] Figure 2 It is a flowchart of the specific implementation manner of the method for judging the single-low form of the fuel cell stack provided by the present invention. SPECIFIC EMBODIMENTS

[0043] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0044] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0045] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention 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 where appropriate for the embodiments of the invention described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0046] This embodiment provides a method for determining the single low-temperature form of a fuel cell stack. Figure 1 A flowchart illustrating the method for determining the single-low form of a fuel cell stack provided by this invention. Figure 1 As shown, the method for determining the single-low form of the fuel cell stack includes:

[0047] Step S1: Obtain the voltage of each individual cell in the fuel cell stack;

[0048] It should be noted that the voltage of each individual cell in the fuel cell stack is obtained through a voltage monitoring instrument (CVM).

[0049] Step S2: Select the single cell with the lowest voltage value and record the voltage value of the single cell with the lowest voltage value as the lowest cell voltage V0;

[0050] Step S3: Calculate the average voltage V2 of the normal cell in the fuel cell stack, and then calculate the difference ΔV between the average voltage V2 of the normal cell and the lowest cell voltage V0.

[0051] Furthermore, the formula for calculating the average voltage V2 of a normal cell in a fuel cell stack is as follows:

[0052]

[0053] Where V is the total voltage of the fuel cell stack, in volts; N is the number of cells in the fuel cell stack; and V0 is the lowest cell voltage.

[0054] Furthermore, the formula for calculating the difference ΔV between the average voltage V2 of the normal battery and the lowest battery voltage V0 is as follows:

[0055] ΔV = V2 - V0.

[0056] Step S4: Obtain the load current density i of the fuel cell stack;

[0057] Step S5: Based on the load current density i of the fuel cell stack, compare the difference ΔV with the maximum voltage loss V1 caused by hydrogen permeation or compare the difference ΔV with the maximum voltage loss V3 caused by mass transfer. Then, determine the single-low form of the fuel cell stack based on the comparison result and output the corresponding control strategy.

[0058] Furthermore, such as Figure 2 As shown, step S5 further includes:

[0059] Determine whether the load current density i of the fuel cell stack is less than a preset value; wherein the preset value is 500 mA / cm². 2 .

[0060] If the load current density i is less than the preset value, the difference ΔV is compared with the maximum voltage loss V1 formed by hydrogen permeation. Then, based on the first comparison result, the single low form of the fuel cell stack is determined, and the corresponding control strategy is output.

[0061] If the load current density i is not less than the preset value, the difference ΔV is compared with the maximum voltage loss V3 formed by the mass transfer. Then, based on the second comparison result, the single low form of the fuel cell stack is determined, and the corresponding control strategy is output.

[0062] Specifically, such as Figure 2 As shown, the step of comparing the difference ΔV with the maximum voltage loss V1 caused by hydrogen permeation, then determining the single-low form of the fuel cell stack based on the first comparison result, and outputting the corresponding control strategy, further includes:

[0063] If ΔV>V1, the single cell with the lowest voltage may have excessive hydrogen permeation, requiring further judgment based on the open-circuit voltage or shutdown.

[0064] If ΔV < V1, the single cell with the lowest voltage may experience limited mass transfer (due to excessive liquid water), requiring an increase in airflow for purging.

[0065] Specifically, such as Figure 2 As shown, the step of comparing the difference ΔV with the maximum voltage loss V3 caused by mass transfer, then determining the single-low form of the fuel cell stack based on the second comparison result, and outputting the corresponding control strategy, further includes:

[0066] If ΔV>V3, the single cell with the lowest voltage may experience severe mass transfer limitation and must be shut down immediately, otherwise it will cause serious irreversible damage to the membrane electrode.

[0067] If ΔV < V3, the operating conditions of the fuel cell stack need to be changed. If the single cell with the lowest voltage value improves, it can continue to operate under the current operating conditions for a period of time. If the single cell with the lowest voltage value still does not improve, it needs to be shut down and purged.

[0068] Furthermore, the formula for calculating the maximum voltage loss V1 caused by hydrogen permeation is as follows:

[0069]

[0070] Where α is the transfer coefficient, which can be obtained from the Tafel equation; i cross This is the hydrogen permeation current density, in A / cm². 2 The value is obtained during membrane electrode detection; i0 is the exchange current density, in A / cm². 2 It can be obtained from the Tafel equation.

[0071] Furthermore, the formula for calculating the maximum voltage loss V3 caused by the mass transfer is as follows:

[0072]

[0073] Among them, i L This is the limiting current density, expressed in A / cm². 2 ; i represents the load current density, in A / cm². 2 .

[0074] Furthermore, the limiting current density i L The calculation formula is as follows:

[0075]

[0076] Where D represents the diffusion coefficient of the reactant component, with units of cm⁻¹. 2 s -1 C represents the total concentration of reactants, in mol / s. -1 δ represents the diffusion distance.

[0077] The method for determining the single-low current density (SLD) condition of a fuel cell stack provided by this invention divides the entire load-bearing condition into two segments based on the current density and the SLD reaction mechanism: low current density (less than 500 mA / cm²). 2 ) and medium to high current density (greater than or equal to 500 mA / cm²) 2 By comparing the difference between the average voltage of a normal cell and the lowest cell voltage collected by CVM with the maximum voltage drop generated under different influencing mechanisms, the single-low voltage scenario can be quickly identified and analyzed under all operating conditions, providing a precise control strategy to reduce membrane electrode damage and extend stack life. Furthermore, this invention can be combined with EIS testing equipment for more accurate analysis.

[0078] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for determining the single-low configuration of a fuel cell stack, characterized in that, The method for determining the single-low form of the fuel cell stack includes: Step S1: Obtain the voltage of each individual cell in the fuel cell stack; Step S2: Select the single cell with the lowest voltage value and record the voltage value of the single cell with the lowest voltage value as the lowest cell voltage V0; Step S3: Calculate the average voltage V2 of the normal cells in the fuel cell stack, and then calculate the difference between the average voltage V2 of the normal cells and the voltage V0 of the lowest cell. ; Step S4: Obtain the load current density i of the fuel cell stack; Step S5: Based on the load current density i of the fuel cell stack, the difference is... Compare with the maximum voltage loss V1 caused by hydrogen permeation or use the difference The voltage drop V3 caused by mass transfer is compared with the voltage drop V3. Based on the comparison result, the single low voltage form of the fuel cell stack is determined and the corresponding control strategy is output. Step S5 further includes: Determine whether the load current density i of the fuel cell stack is less than a preset value; If the load current density i is less than the preset value, then the difference will be... The voltage drop V1 caused by hydrogen permeation is compared with the voltage drop V1, and then the single low form of the fuel cell stack is determined based on the first comparison result, and the corresponding control strategy is output. If the load current density i is not less than the preset value, then the difference will be... The voltage drop V3 caused by the mass transfer is compared with the voltage drop V3. Then, based on the second comparison result, the single low form of the fuel cell stack is determined and the corresponding control strategy is output. The preset value is 500 mA / cm. 2 .

2. The method for determining the single-low configuration of a fuel cell stack according to claim 1, characterized in that, The formula for calculating the maximum voltage loss V1 caused by hydrogen permeation is as follows: in, For the transfer coefficient, The hydrogen permeation current density, For exchange current density.

3. The method for determining the single-low configuration of a fuel cell stack according to claim 1, characterized in that, The formula for calculating the maximum voltage drop V3 caused by the mass transfer is as follows: in, Let be the limiting current density, and i be the tensile current density.

4. The method for determining the single-low configuration of a fuel cell stack according to claim 3, characterized in that, The limiting current density The calculation formula is as follows: Where D represents the diffusion coefficient of the reactant component, and C represents the total concentration of the reactants. Indicates the diffusion distance.

5. The method for determining the single-low configuration of a fuel cell stack according to claim 1, characterized in that, The formula for calculating the average voltage V2 of a normal cell in the fuel cell stack is as follows: Where V is the total voltage of the fuel cell stack, N is the number of cells in a single fuel cell stack, and V0 is the lowest cell voltage.

6. The method for determining the single-low configuration of a fuel cell stack according to claim 1, characterized in that, The difference between the average voltage V2 of the normal battery and the lowest battery voltage V0 The calculation formula is as follows: 。 7. The method for determining the single-low configuration of a fuel cell stack according to claim 1, characterized in that, The difference The system compares the voltage drop V1 caused by hydrogen permeation with the voltage drop value V1, then determines the single-low voltage configuration of the fuel cell stack based on the first comparison result, and outputs the corresponding control strategy. The system also includes: like >V1, at this point the single cell with the lowest voltage value has excessive hydrogen leakage, and further judgment or shutdown is required by checking the open circuit voltage. like <V1, at this point the single cell with the lowest voltage value experiences limited mass transfer and requires increased airflow for purging.

8. The method for determining the single-low configuration of a fuel cell stack according to claim 1, characterized in that, The difference The process includes comparing the voltage drop V3 caused by the mass transfer with the voltage drop V3, determining the single-low configuration of the fuel cell stack based on the second comparison result, and outputting the corresponding control strategy. The process also includes: like >V3, at which point the single cell with the lowest voltage value experiences severely limited mass transfer and needs to be shut down immediately; like <V3, at this point the operating conditions of the fuel cell stack need to be changed. If the single cell with the lowest voltage value improves, then run under the current operating conditions for a period of time. If the single cell with the lowest voltage value still does not improve, then the unit needs to be shut down and purged.

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