Fuel cell stack water content monitoring method, device, system and storage medium

Abstract

The application discloses a fuel cell stack water content monitoring method, device, system and storage medium. The absolute value of the difference between the calculated value of the high-frequency impedance and the measured value of the high-frequency impedance is calculated. If the absolute value is greater than the error threshold, the initial water content is continuously updated according to the preset rule until the absolute value of the difference between the calculated value of the high-frequency impedance of the fuel cell obtained according to the relationship between the updated initial water content, the stack temperature and the high-frequency impedance of the fuel cell and the measured value of the high-frequency impedance is not greater than the error threshold. The updated initial water content is set as the reference water content of the fuel cell. The calculated value of the high-frequency impedance and the measured value of the high-frequency impedance are obtained under the same stack temperature condition, so the stack temperature will not produce error. When the error is small, the updated initial water content is close to the real water content of the fuel cell stack, and the reference water content can more accurately represent the real water content of the fuel cell stack.

Description

Technical Field

[0001] This application relates to the field of fuel cell technology, and more specifically, to a method, apparatus, system, and storage medium for monitoring the water content of a fuel cell stack. Background Technology

[0002] A fuel cell is an electrochemical reaction device that directly converts the chemical energy in fuel and oxidant into electrical energy. A proton exchange membrane fuel cell is one type of fuel cell that uses hydrogen as fuel, air or oxygen as an oxidant, and water as a reaction product. It boasts advantages such as high efficiency, being green and environmentally friendly, and being able to start at low temperatures. It can be used as a power source for mobile vehicles such as automobiles, airplanes, and submarines, as well as for telecommunications base stations and distributed power stations.

[0003] The power generation unit of a proton exchange membrane fuel cell (PEMFC) is the membrane electrode assembly (MEA). The MEA consists of a proton exchange membrane, a catalyst layer, and a diffusion layer. The proton exchange membrane plays a crucial role in conducting protons, isolating fuel and oxidant, and isolating electrons. Water is required for proton conduction, and the MEA is sensitive to the humidity of the reactant gases. Excessive humidity can lead to flooding, while insufficient humidity can cause membrane drying. Frequent flooding and drying not only affect the performance of the fuel cell but also shorten its lifespan. Therefore, monitoring the water content of the fuel cell stack is essential to ensure both performance and lifespan.

[0004] Current fuel cell stack water content monitoring technology assumes a correlation between the fuel cell's high-frequency impedance and the stack's water content, thus indirectly characterizing the water content through high-frequency impedance. The measured high-frequency impedance is compared to a set impedance threshold to determine the proton exchange membrane's (PEM) wet / dry state. A measured high-frequency impedance less than or equal to the threshold indicates a wet PEM, while a measured impedance greater than the threshold indicates a dry PEM. However, this method only provides a preliminary assessment of the PEM's wet / dry state and cannot precisely determine the degree of wetness or dryness. Summary of the Invention

[0005] In view of this, this application provides a method, apparatus, system and storage medium for monitoring the water content of fuel cell stacks, which solves the problem that existing methods for monitoring the water content of fuel cell stacks can only preliminarily determine whether the proton exchange membrane is dry or wet, and cannot accurately determine the degree of wetness or dryness of the proton exchange membrane.

[0006] To achieve the above objectives, the following solution is proposed:

[0007] A method for monitoring water content in a fuel cell stack, comprising:

[0008] Set the initial water content of the fuel cell stack;

[0009] The high-frequency impedance of the fuel cell and the stack temperature of the fuel cell stack are obtained.

[0010] The calculated value of the high-frequency impedance of the fuel cell is obtained by calculating the relationship between the initial water content, the stack temperature, and the high-frequency impedance of the fuel cell.

[0011] Calculate the absolute value of the difference between the calculated value of the high-frequency impedance and the measured value of the high-frequency impedance;

[0012] If the absolute value is greater than the preset error threshold, the initial water content is updated according to the preset rules until the absolute value of the difference between the calculated value of the high-frequency impedance of the fuel cell, obtained by calculating the relationship between the updated initial water content, the stack temperature and the high-frequency impedance of the fuel cell and the measured value of the high-frequency impedance is not greater than the preset error threshold.

[0013] The updated initial water content is set as the reference water content for the fuel cell.

[0014] Preferably, the calculated value of the high-frequency impedance of the fuel cell is obtained by calculating the relationship between the initial water content, the stack temperature, and the high-frequency impedance of the fuel cell, including:

[0015] The proton exchange membrane conductivity of the fuel cell is calculated based on the relationship between the initial water content, the stack temperature, and the proton exchange membrane conductivity of the fuel cell.

[0016] The calculated value of the high-frequency impedance of the fuel cell is obtained by calculating the relationship between the conductivity of the proton exchange membrane and the high-frequency impedance of the fuel cell.

[0017] Preferably, before calculating the proton exchange membrane conductivity of the fuel cell based on the relationship between the initial water content, the stack temperature, and the proton exchange membrane conductivity of the fuel cell, the method further includes:

[0018] Based on the initial water content, a first relationship is determined, which is the relationship between the water content of the fuel cell stack, the temperature of the fuel cell stack, and the conductivity of the proton exchange membrane of the fuel cell.

[0019] The calculation of the proton exchange membrane conductivity of the fuel cell based on the relationship between the initial water content and the stack temperature includes:

[0020] The initial water content and the stack temperature are substituted into the first relationship to calculate the proton exchange membrane conductivity of the fuel cell.

[0021] Preferably, determining the first relationship corresponding to the initial water content based on the initial water content includes:

[0022] If the initial water content is less than the first value, then the first relationship corresponding to the initial water content is:

[0023]

[0024] Where σ is the proton exchange membrane conductivity of the fuel cell, p is the first value, T is the fuel cell stack temperature, k is the temperature conversion coefficient, and a, b, c, and n are coefficients obtained by fitting through experimental measurements.

[0025] If the initial water content is greater than or equal to the first value and less than or equal to the second value, then the first relationship corresponding to the initial water content is:

[0026]

[0027] Wherein, λ represents the water content of the fuel cell stack;

[0028] If the initial water content is greater than the second value, then the first relationship corresponding to the initial water content is:

[0029]

[0030] Wherein, σ(m, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is m, m is the second value, σ(x, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is x, σ(xy, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is xy, x and y are coefficients obtained by fitting based on experimental measurements, and 0 < y < 1, x <m。

[0031] Preferably, the calculated value of the high-frequency impedance of the fuel cell is obtained by calculating the relationship between the conductivity of the proton exchange membrane and the high-frequency impedance of the fuel cell, including:

[0032] The ionic impedance of the proton exchange membrane of the fuel cell is calculated based on the relationship between the conductivity of the proton exchange membrane and the ionic impedance of the proton exchange membrane.

[0033] The ohmic impedance of the fuel cell proton conductor is calculated based on the relationship between the ionic impedance of the fuel cell proton exchange membrane and the ohmic impedance of the fuel cell proton conductor.

[0034] The calculated value of the high-frequency impedance of the fuel cell is obtained by calculating the relationship between the ohmic impedance of the proton conductor and the high-frequency impedance of the fuel cell.

[0035] Preferably, before calculating the high-frequency impedance of the fuel cell based on the relationship between the initial water content, the stack temperature, and the high-frequency impedance of the fuel cell, the method further includes:

[0036] Determine whether the initial water content is less than the third value;

[0037] If the initial water content is less than the third value, then the step of calculating the high-frequency impedance of the fuel cell based on the relationship between the initial water content, the stack temperature, and the high-frequency impedance of the fuel cell is performed.

[0038] A fuel cell stack water content monitoring device, comprising:

[0039] A water content setting unit is used to set the initial water content of the fuel cell stack;

[0040] The measurement acquisition unit is used to acquire the measured value of the high-frequency impedance of the fuel cell and the stack temperature of the fuel cell stack;

[0041] A high-frequency impedance calculation unit is used to calculate the high-frequency impedance of the fuel cell based on the relationship between the initial water content, the stack temperature and the high-frequency impedance of the fuel cell.

[0042] An error calculation unit is used to calculate the absolute value of the difference between the calculated value of the high-frequency impedance and the measured value of the high-frequency impedance.

[0043] If the absolute value is greater than a preset error threshold, then the following steps of the water content update unit are executed; if the absolute value is not greater than the preset error threshold, then the following steps of the reference water content setting unit are executed.

[0044] A water content update unit is used to update the initial water content according to a preset rule and return to the step of executing the high-frequency impedance calculation unit;

[0045] A reference water content setting unit is used to set the updated initial water content as the reference water content of the fuel cell.

[0046] Preferably, the high-frequency impedance calculation unit includes:

[0047] The conductivity calculation subunit is used to calculate the conductivity of the fuel cell proton exchange membrane based on the relationship between the initial water content, the stack temperature and the conductivity of the fuel cell proton exchange membrane.

[0048] The high-frequency impedance calculation subunit is used to calculate the high-frequency impedance of the fuel cell based on the relationship between the conductivity of the proton exchange membrane and the high-frequency impedance of the fuel cell.

[0049] A fuel cell stack water content monitoring system includes: a DC voltage converter and a fuel cell controller;

[0050] The DC-DC voltage converter includes: a digital signal processor, a current sensor, and a signal conditioning circuit;

[0051] The fuel cell controller includes: an analog-to-digital converter and a microcontroller;

[0052] The digital signal processor is used to superimpose an excitation current at the output terminal of the fuel cell stack.

[0053] The current sensor is used to measure the bus current at the output terminal of the fuel cell stack and transmit the bus current to the signal conditioning circuit.

[0054] The signal conditioning circuit is used to measure the bus voltage at the output terminal of the fuel cell stack, modulate the bus voltage and the bus current, and input the modulated bus current and the modulated bus voltage into the analog-to-digital converter.

[0055] The analog-to-digital converter is used to sample the modulated bus current and the modulated bus voltage respectively to obtain sampled current and sampled voltage, extract the target current and target voltage in the target frequency domain, and transmit the target current and target voltage to the microcontroller.

[0056] The microcontroller is used to calculate the measured value of the high-frequency impedance of the fuel cell based on the target current and the target voltage, and to execute each step of the aforementioned fuel cell stack water content monitoring method.

[0057] A storage medium storing a computer program, which, when executed by a processor, implements the various steps of the aforementioned fuel cell stack water content monitoring method.

[0058] As can be seen from the above technical solution, the fuel cell stack water content monitoring method provided in this application pre-sets the initial water content and error threshold of the fuel cell stack. First, it obtains the measured value of the high-frequency impedance of the fuel cell and the stack temperature of the fuel cell stack. Existing technology considers that the high-frequency impedance of the fuel cell is only related to the water content of the fuel cell stack, thus indirectly characterizing the water content of the fuel cell stack through the high-frequency impedance. The inventors of this application consider that the high-frequency impedance of the fuel cell is affected not only by the stack water content but also by the stack temperature. Therefore, this application also sets the stack temperature as a variable, experimentally determining the relationship between the high-frequency impedance, stack water content, and stack temperature. Then, based on the relationship between the initial water content, stack temperature, and high-frequency impedance of the fuel cell, the calculated value of the high-frequency impedance of the fuel cell is obtained. The difference between the calculated value and the measured value of the high-frequency impedance is then calculated, and the absolute value of the difference is taken to obtain the error between the calculated and measured values ​​of the high-frequency impedance. Because the calculated value of the high-frequency impedance is obtained based on the relationship between the initial water content, stack temperature, and high-frequency impedance of the fuel cell, the influence of the stack temperature is taken into account. Since the calculated and measured values ​​of high-frequency impedance are obtained under the same stack temperature conditions, the stack temperature will not introduce errors. When the error exceeds the error threshold, it indicates a significant difference between the initial water content and the actual water content of the current fuel cell stack. In this case, the initial water content is updated according to preset rules. When the error between the calculated and measured values ​​of the high-frequency impedance of the fuel cell, calculated based on the relationship between the updated initial water content, stack temperature, and fuel cell high-frequency impedance, is no greater than the error threshold, the updated initial water content is set as the reference water content of the fuel cell stack. Because the stack temperature does not introduce errors, when the error is small, the updated initial water content is close to the actual water content of the fuel cell stack. Therefore, the reference water content can more accurately characterize the actual water content of the fuel cell stack.

[0059] Furthermore, considering the potentially complex relationship between fuel cell stack water content, stack temperature, and high-frequency impedance, deriving the water content from the measured high-frequency impedance and stack temperature using this relationship would place high demands on the computing power of the instruments. This application employs a trial-and-error method, continuously adjusting the initial water content. Based on the adjusted initial water content and stack temperature, the high-frequency impedance is calculated according to the aforementioned relationship, and the error is compared with the measured high-frequency impedance value. The process continues until the error is no greater than an error threshold, indicating that the adjusted initial water content is close to the actual water content. This trial-and-error method requires less computing power, thus further expanding the applicability of this application. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0061] Figure 1 A schematic diagram of an optional fuel cell stack water content monitoring system provided for an embodiment of this application;

[0062] Figure 2 A flowchart of a method for monitoring water content in a fuel cell stack provided in this application embodiment;

[0063] Figure 3 A graph showing the relationship between the water content of the fuel cell stack and its high-frequency impedance at a fixed temperature is provided for an embodiment of this application.

[0064] Figure 4 A graph showing the relationship between the water content of the fuel cell stack and the conductivity of the proton exchange membrane provided in an embodiment of this application;

[0065] Figure 5 A schematic diagram of a fuel cell structure provided in an embodiment of this application;

[0066] Figure 6 This is a schematic diagram of a fuel cell stack water content monitoring device provided in an embodiment of this application. Detailed Implementation

[0067] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0068] This application provides a water content monitoring scheme for fuel cell stacks, applicable to stacks composed of multiple proton exchange membrane fuel cells. First, an optional fuel cell stack water content monitoring system provided in this application is introduced. For example... Figure 1 As shown in the embodiment of this application, the fuel cell stack water content monitoring system includes: a DC voltage converter and a fuel cell controller. The DC voltage converter consists of a digital signal processor and a signal conditioning circuit, while the fuel cell controller consists of an analog-to-digital converter and a microcontroller.

[0069] A digital signal processor (DSP) is used to superimpose an excitation current onto the output of a fuel cell stack. This excitation current can be sinusoidal, cosine, or other similar types. For example, after receiving an instruction, the DSP in a DC-DC converter superimposes a sinusoidal excitation current of a certain amplitude (e.g., 3A) and a certain frequency (e.g., 1000Hz) onto the DC output of the fuel cell stack.

[0070] A current sensor is used to measure the bus current at the output end of the fuel cell stack and transmit the bus current to the signal conditioning circuit.

[0071] The signal conditioning circuit measures the bus voltage at the output terminal of the fuel cell stack and modulates the bus voltage and bus current. Modulation can involve isolating the DC component of the bus current and voltage while retaining the AC component, and modulating the amplitude of the bus voltage. The modulated bus current and voltage are then input to the analog-to-digital converter (ADC). For example, the signal conditioning circuit measures the bus voltage, and a current sensor measures the bus current at the fuel cell stack output terminal and transmits it to the signal conditioning circuit. The signal conditioning circuit then isolates the DC component from the bus current and voltage, retaining only the AC component of a certain frequency (e.g., 1000Hz), and modulates the retained AC component signal strength to a certain amplitude range (e.g., 0-5V) before transmitting it to the ADC built into the fuel cell controller.

[0072] An analog-to-digital converter (ADC) is used to sample the modulated bus current and voltage separately, obtaining sampled current and voltage, and extracting the target current and voltage within the target frequency range. These target current and voltage are then transmitted to the microcontroller. For example, the ADC can acquire the modulated bus current and voltage analog signals transmitted by the signal conditioning circuit at a certain sampling frequency (e.g., 8000Hz), continuously acquiring a certain number (e.g., 1024) data points for each. After acquisition, a time-frequency transformation algorithm is used to transform the time-domain signal to a frequency-domain signal, and then the target current and voltage within the target frequency range (e.g., 1000Hz) of the voltage and current signal frequency domain sequences are extracted and transmitted to the microcontroller.

[0073] The microcontroller is used to calculate the measured value of the high-frequency impedance of the fuel cell based on the target current and target voltage, and to calculate the calculated value of the high-frequency impedance of the fuel cell based on the initial water content and stack temperature. It calculates the error between the measured value and the calculated value of the high-frequency impedance. When the error is greater than the error threshold, it continuously updates the initial water content until the error is no greater than the error threshold, and sets the updated initial water content as the reference water content.

[0074] This application provides a fuel cell stack water content monitoring system, which mainly includes a DC-DC converter and a fuel cell controller. The DC-DC converter consists of a digital signal processor, a current sensor, and a signal conditioning circuit. The fuel cell controller consists of an analog-to-digital converter and a microcontroller. This system measures the fuel cell stack bus current and voltage, modulates the measured current and voltage, processes the modulated signals to obtain a measured high-frequency impedance, and then calculates the high-frequency impedance based on the initial water content and stack temperature. The system calculates the error between the measured and calculated high-frequency impedance values. Since both values ​​are obtained under the same stack temperature, there is no error due to the stack temperature. Therefore, when the error exceeds a threshold, the initial water content is continuously updated until the error is no greater than the threshold. The updated initial water content is then set as the reference water content. At this point, the updated initial water content is close to the actual water content of the fuel cell stack, and the reference water content more accurately represents the actual water content of the fuel cell stack.

[0075] Combination Figure 2 This paper introduces the fuel cell stack water content monitoring method provided in the embodiments of this application from the perspective of microcontrollers, such as... Figure 2 As shown, the method may include:

[0076] Step S01: Set the initial water content of the fuel cell stack.

[0077] Specifically, the water content of a fuel cell stack typically falls within a certain range, so a suitable value can be chosen as the initial water content of the fuel cell stack. The minimum value within this range can be set as the initial water content, the maximum value within the range can be set as the initial water content, or a value within or outside the range can be selected as the initial water content. For example, taking the minimum value within this range as the initial water content of the fuel cell stack, if 2 ≤ λ ≤ 14, where λ is the water content of the stack, then the initial water content can be set to 2.

[0078] Step S02: Obtain the measured value of the high-frequency impedance of the fuel cell and the stack temperature of the fuel cell stack.

[0079] Specifically, the analog-to-digital converter transmits the target current and target voltage to the microcontroller. Therefore, the microcontroller can calculate the measured value of the fuel cell's high-frequency impedance based on the target current and target voltage. Since the high-frequency impedance of the fuel cell is affected by the stack temperature, the stack temperature of the fuel cell stack, transmitted by temperature sensors and other temperature measuring instruments, can also be obtained.

[0080] Step S03: Calculate the high-frequency impedance of the fuel cell based on the relationship between the initial water content, stack temperature, and high-frequency impedance of the fuel cell.

[0081] Specifically, Figure 3 To establish a fixed stack temperature and understand the relationship between the fuel cell's water content and its high-frequency impedance, and considering that the high-frequency impedance is affected not only by the stack water content but also by the stack temperature, we set the fuel cell's high-frequency impedance, water content, and temperature as variables. Through experimental fitting, we obtained the relationship between these three parameters. Therefore, after setting the initial water content and measuring the stack temperature, we can calculate the high-frequency impedance of the fuel cell based on the experimentally obtained relationship.

[0082] Step S04: Calculate the absolute value of the difference between the calculated value of the high-frequency impedance and the measured value of the high-frequency impedance.

[0083] Specifically, because the calculated high-frequency impedance value takes into account the influence of the fuel cell stack temperature, and both the calculated and measured high-frequency impedance values ​​are obtained under the same stack temperature conditions, the stack temperature does not introduce error. Therefore, the difference between the calculated and measured high-frequency impedance values ​​can be calculated, and the absolute value of this difference can be taken to obtain the error between the calculated and measured high-frequency impedance values. Since the stack temperature does not introduce error, the error between the calculated and measured high-frequency impedance values ​​can represent the error between the initial and actual water content of the fuel cell.

[0084] Step S05: If the absolute value is greater than the preset error threshold, the initial water content is updated according to the preset rules until the absolute value of the difference between the calculated value of the high-frequency impedance of the fuel cell, obtained by calculating the relationship between the updated initial water content, stack temperature and high-frequency impedance of the fuel cell, and the measured value of the high-frequency impedance is not greater than the preset error threshold.

[0085] Specifically, when the absolute value is greater than the preset threshold, it indicates that there is a large difference between the initial water content and the actual water content. Therefore, it is necessary to update the value of the initial water content so that the initial water content gradually approaches the actual water content. When the absolute value of the difference between the calculated value of the high-frequency impedance of the fuel cell, obtained by calculating the relationship between the updated initial water content, the stack temperature, and the high-frequency impedance of the fuel cell, and the measured value of the high-frequency impedance is not greater than the preset error threshold, it proves that the updated initial water content is very close to the actual water content. At this time, the update of the initial water content can be stopped.

[0086] Updating the initial water content according to preset rules can be done by increasing or decreasing the initial water content by a preset step size. For example, if the minimum value of the water content range is set as the initial water content, the preset step size can be increased based on the minimum value; if the maximum value of the water content range is set as the initial water content, the preset step size can be decreased based on the maximum value.

[0087] Step S06: Set the updated initial water content as the reference water content for the fuel cell.

[0088] Specifically, since the stack temperature does not produce errors, when the error is small, the updated initial water content is close to the actual water content of the fuel cell stack. Therefore, the updated initial water content can be set as the reference water content of the fuel cell stack. In this case, the reference water content can more accurately characterize the actual water content of the fuel cell stack.

[0089] The fuel cell stack water content monitoring method provided in this application pre-sets the initial water content and error threshold of the fuel cell stack. First, it acquires the measured value of the high-frequency impedance of the fuel cell and the stack temperature. Existing technology considers the high-frequency impedance of a fuel cell to be only related to the water content of the fuel cell stack, thus indirectly characterizing the water content through the high-frequency impedance. The inventors of this application consider that the high-frequency impedance of the fuel cell is affected not only by the stack water content but also by the stack temperature. Therefore, this application also sets the stack temperature as a variable, experimentally determining the relationship between the high-frequency impedance, stack water content, and stack temperature. Then, based on the relationship between the initial water content, stack temperature, and high-frequency impedance, the calculated value of the high-frequency impedance is obtained. The difference between the calculated value and the measured value of the high-frequency impedance is then calculated, and the absolute value of the difference is taken to obtain the error between the calculated and measured values. Because the calculated value of the high-frequency impedance is obtained based on the relationship between the initial water content, stack temperature, and high-frequency impedance, the influence of the stack temperature is taken into account. Since the calculated and measured values ​​of high-frequency impedance are obtained under the same stack temperature conditions, the stack temperature will not introduce errors. When the error exceeds the error threshold, it indicates a significant difference between the initial water content and the actual water content of the current fuel cell stack. In this case, the initial water content is updated according to preset rules. When the error between the calculated and measured values ​​of the high-frequency impedance of the fuel cell, calculated based on the relationship between the updated initial water content, stack temperature, and fuel cell high-frequency impedance, is no greater than the error threshold, the updated initial water content is set as the reference water content of the fuel cell stack. Because the stack temperature does not introduce errors, when the error is small, the updated initial water content is close to the actual water content of the fuel cell stack. Therefore, the reference water content can more accurately characterize the actual water content of the fuel cell stack.

[0090] Furthermore, considering the potentially complex relationship between fuel cell stack water content, stack temperature, and high-frequency impedance, deriving the water content from the measured high-frequency impedance and stack temperature using this relationship would place high demands on the computing power of the instruments. This application employs a trial-and-error method, continuously adjusting the initial water content. Based on the adjusted initial water content and stack temperature, the high-frequency impedance is calculated according to the aforementioned relationship, and the error is compared with the measured high-frequency impedance value. The process continues until the error is no greater than an error threshold, indicating that the adjusted initial water content is close to the actual water content. This trial-and-error method requires less computing power, thus further expanding the applicability of this application.

[0091] This application embodiment describes the process of calculating the high-frequency impedance of the fuel cell in step S03 based on the relationship between the initial water content, the stack temperature, and the high-frequency impedance of the fuel cell. The process may include:

[0092] Step S031: The proton exchange membrane conductivity of the fuel cell is calculated based on the relationship between the initial water content, the stack temperature and the proton exchange membrane conductivity of the fuel cell.

[0093] Specifically, Figure 4 To establish a fixed stack temperature, the relationship between the stack water content and the proton exchange membrane conductivity of the fuel cell was experimentally fitted. Furthermore, by setting the stack temperature as a variable, the relationship between the stack water content, stack temperature, and the proton exchange membrane conductivity of the fuel cell can be experimentally determined. Therefore, based on the set initial water content and the measured stack temperature, the proton exchange membrane conductivity of the fuel cell can be calculated.

[0094] Step S032: Calculate the high-frequency impedance of the fuel cell based on the relationship between the conductivity of the proton exchange membrane and the high-frequency impedance of the fuel cell.

[0095] Specifically, the relationship between the proton exchange membrane conductivity and the high-frequency impedance of a fuel cell can be derived. Therefore, after obtaining the proton exchange membrane conductivity, the high-frequency impedance of the fuel cell can be calculated based on it.

[0096] In step S031 of this embodiment, the proton exchange membrane conductivity of the fuel cell is calculated based on the relationship between the initial water content, the stack temperature and the proton exchange membrane conductivity of the fuel cell. Before that, step S033 can also be performed.

[0097] Step S033: Determine the first relational expression corresponding to the initial water content based on the initial water content.

[0098] Specifically, the relationships between the proton exchange membrane (PEM), stack temperature, and PEM conductivity obtained from experimental fitting differ depending on the range of water content in the fuel cell stack. Therefore, before calculating the PEM conductivity, it is necessary to determine the first relationship between the initial water content, fuel cell stack temperature, and PEM conductivity based on the initial water content.

[0099] The water content of the fuel cell stack is generally maintained within a certain range. Therefore, two values ​​can be set to divide the range into three parts, where the first value is less than the second value.

[0100] like Figure 4As shown, the lower the initial water content, the closer the proton exchange membrane conductivity of the fuel cell is to 0, and the smaller the change in proton exchange membrane conductivity. Therefore, the initial water content can be set as the first value, and then the proton exchange membrane conductivity of the fuel cell can be calculated. Thus, the first relationship corresponding to the initial water content is:

[0101]

[0102] Where σ is the proton exchange membrane conductivity of the fuel cell, p is the first value, T is the fuel cell stack temperature, k is the temperature conversion coefficient, and a, b, c, and n are coefficients obtained by fitting through experimental measurements.

[0103] When the initial water content is greater than or equal to the first value and less than or equal to the second value, the initial water content is in an intermediate range, such as... Figure 4 As shown, when the water content in the fuel cell stack is within the intermediate range, the conductivity of the proton exchange membrane exhibits a positive correlation with increasing water content. Based on experimental fitting, the first relationship corresponding to the initial water content can be obtained as follows:

[0104]

[0105] Where λ represents the water content of the fuel cell stack.

[0106] When the initial water content is greater than the second value, the initial water content is relatively large, such as... Figure 4 As shown, when the water content of the fuel cell stack is high, the conductivity tends to a constant. Through experimental fitting, the first relationship corresponding to the initial water content can be obtained as follows:

[0107]

[0108] Where σ(m, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is m, m is a second value; σ(x, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is x; σ(xy, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is xy; x and y are coefficients obtained by fitting experimental measurements, and 0 < y < 1. <m。

[0109] Based on this, step S031, which calculates the proton exchange membrane conductivity of the fuel cell according to the relationship between the initial water content, the stack temperature, and the proton exchange membrane conductivity of the fuel cell, can be as follows:

[0110] Substituting the initial water content and stack temperature into the first relationship, the conductivity of the fuel cell proton exchange membrane is obtained.

[0111] Specifically, by substituting the initial water content and stack temperature into the first relationship corresponding to the initial water content, the conductivity of the fuel cell proton exchange membrane can be calculated.

[0112] This application embodiment describes the process of calculating the high-frequency impedance of the fuel cell in step S032 based on the relationship between the conductivity of the proton exchange membrane and the high-frequency impedance of the fuel cell. The process may include:

[0113] Step S0321: Calculate the ionic impedance of the proton exchange membrane of the fuel cell based on the relationship between the conductivity of the proton exchange membrane and the ionic impedance of the proton exchange membrane.

[0114] Specifically, since there is an inverse relationship between the conductivity and ionic impedance of the proton exchange membrane in a fuel cell, and the conductivity of the proton exchange membrane has been calculated, the ionic impedance of the proton exchange membrane in the fuel cell can be calculated.

[0115] Step S0322: Calculate the ohmic impedance of the fuel cell proton conductor based on the relationship between the ionic impedance of the fuel cell proton exchange membrane and the ohmic impedance of the fuel cell proton conductor.

[0116] Specifically, the ohmic impedance of the proton conductor in a fuel cell is composed of the ionic impedance of the proton exchange membrane and the ionic impedance of the catalyst layer. Therefore, the ohmic impedance of the proton conductor can be the sum of the ionic impedance of the proton exchange membrane and the ionic impedance of the catalyst layer.

[0117] Since the resin in the catalyst layer and the resin in the proton exchange membrane are made of the same material, under similar water content conditions, the ionic impedance of the proton exchange membrane and the ionic impedance of the catalyst layer depend only on the proton transport distance. Figure 5 As shown, 1 is the cathode catalyst layer of the fuel cell, 2 is the proton exchange membrane (PEM) of the fuel cell, 3 is the anode catalyst layer of the fuel cell, 4 and 5 are gas diffusion layers, 6 is the cathode plate, 7 is the anode plate, d1 is the proton transport distance within the catalyst layer, and d2 is the proton transport distance within the PEM. The proton transport distance depends on the fabrication process and parameters of the catalyst layer and the PEM, so the proton transport distance can be determined, and the relationship between the proton transport distances is linear. Therefore, the ionic impedance of the PEM and the ionic impedance of the catalyst layer can be approximated as linear, and the linear coefficient and offset can be obtained through experimentation. Therefore, the ionic impedance of the catalyst layer can be represented by the ionic impedance of the PEM, and thus the relationship between the ionic impedance of the PEM and the ohmic impedance of the proton conductor of the fuel cell can be obtained. Then, based on the calculated ionic impedance of the PEM, the ohmic impedance of the proton conductor of the fuel cell can be further calculated.

[0118] Step S0323: Calculate the high-frequency impedance of the fuel cell by considering the relationship between the ohmic impedance of the proton conductor and the high-frequency impedance of the fuel cell.

[0119] Specifically, the high-frequency impedance of a fuel cell represents the total ohmic impedance of the fuel cell, which includes the ohmic impedance of the proton conductor and the ohmic impedance of the electronic conductor. Therefore, the high-frequency impedance of a fuel cell is the sum of the ohmic impedances of the proton conductor and the electronic conductor. Because the ohmic impedance of the electronic conductor is relatively stable, it can be directly obtained through experimental measurement. Based on the obtained ohmic impedances of the proton conductor and the electronic conductor, the calculated value of the high-frequency impedance of the fuel cell can be obtained.

[0120] In this embodiment of the application, before calculating the high-frequency impedance of the fuel cell based on the relationship between the initial water content, the stack temperature, and the high-frequency impedance of the fuel cell in step S03, the following step S07 can also be performed.

[0121] Step S07: Determine whether the initial water content is less than the third value.

[0122] Specifically, fuel cells cannot function properly when the water content is too high. Therefore, the water content in a fuel cell stack is generally maintained within a certain range. A third value can be preset as a value greater than the second value, and the initial water content can be judged to be reasonable by checking whether it is less than the third value.

[0123] When the initial water content is set to be greater than or equal to the third value, the process of decreasing the initial water content by a preset step size to determine the reference water content may result in numerous calculation steps during the trial-and-error process. In this case, the user can be prompted to reset the initial water content. When the initial water content is set to be less than or equal to the first value, the initial water content is increased by a preset step size. When the initial water content is greater than or equal to the third value, the reference water content obtained through further trial-and-error will be greater than or equal to the third value, exceeding the range of water content suitable for normal operation of the fuel cell, and increasing the calculation steps. At this point, the trial-and-error process can be stopped. When the initial water content is less than the third value, step S03 is executed, which calculates the high-frequency impedance of the fuel cell based on the relationship between the initial water content, the stack temperature, and the high-frequency impedance of the fuel cell.

[0124] In this embodiment, before calculating the high-frequency impedance of the fuel cell based on the relationship between the initial water content, the stack temperature, and the fuel cell, the initial water content is first determined. Calculation is only performed when the initial water content is within a suitable range, reducing unnecessary calculations and improving the efficiency of fuel cell stack water content monitoring.

[0125] The fuel cell stack water content monitoring device provided in the embodiments of this application is described below. The fuel cell stack water content monitoring device described below can be referred to in correspondence with the fuel cell stack water content monitoring method described above.

[0126] First, combine Figure 6 This section introduces a water content monitoring device for fuel cell stacks, such as... Figure 6 As shown, the fuel cell stack water content monitoring device may include:

[0127] Water content setting unit 100 is used to set the initial water content of the fuel cell stack;

[0128] The measurement acquisition unit 200 is used to acquire the measured value of the high-frequency impedance of the fuel cell and the stack temperature of the fuel cell stack.

[0129] The high-frequency impedance calculation unit 300 is used to calculate the high-frequency impedance of the fuel cell based on the relationship between the initial water content, the stack temperature and the high-frequency impedance of the fuel cell.

[0130] Error calculation unit 400 is used to calculate the absolute value of the difference between the calculated value of the high-frequency impedance and the measured value of the high-frequency impedance;

[0131] If the absolute value is greater than a preset error threshold, then the following steps of the water content update unit are executed; if the absolute value is not greater than the preset error threshold, then the following steps of the reference water content setting unit are executed.

[0132] The water content update unit 500 is used to update the initial water content according to a preset rule and return to the step of executing the high-frequency impedance calculation unit;

[0133] The reference water content setting unit 600 is used to set the updated initial water content as the reference water content of the fuel cell.

[0134] Optionally, the high-frequency impedance calculation unit includes:

[0135] The conductivity calculation subunit is used to calculate the conductivity of the fuel cell proton exchange membrane based on the relationship between the initial water content, the stack temperature and the conductivity of the fuel cell proton exchange membrane.

[0136] The high-frequency impedance calculation subunit is used to calculate the high-frequency impedance of the fuel cell based on the relationship between the conductivity of the proton exchange membrane and the high-frequency impedance of the fuel cell.

[0137] Optionally, the high-frequency impedance calculation unit further includes:

[0138] The relational formula determination subunit is used to determine the first relational formula corresponding to the initial water content before the conductivity calculation subunit calculates the conductivity of the fuel cell proton exchange membrane based on the relationship between the initial water content, the stack temperature and the conductivity of the fuel cell. The first relational formula is the relationship between the fuel cell stack water content, the fuel cell stack temperature and the fuel cell proton exchange membrane conductivity.

[0139] Based on this, the conductivity calculation subunit calculates the conductivity of the fuel cell proton exchange membrane according to the relationship between the initial water content, the stack temperature, and the conductivity of the fuel cell proton exchange membrane. This process may include:

[0140] The initial water content and the stack temperature are substituted into the first relationship to calculate the proton exchange membrane conductivity of the fuel cell.

[0141] Optionally, the process by which the relationship determination subunit determines the first relationship corresponding to the initial water content based on the initial water content, wherein the first relationship is the relationship between the fuel cell stack water content, the fuel cell stack temperature, and the fuel cell proton exchange membrane conductivity, may include:

[0142] If the initial water content is less than the first value, then the first relationship corresponding to the initial water content is:

[0143]

[0144] Where σ is the proton exchange membrane conductivity of the fuel cell, p is the first value, T is the fuel cell stack temperature, k is the temperature conversion coefficient, and a, b, c, and n are coefficients obtained by fitting through experimental measurements.

[0145] If the initial water content is greater than or equal to the first value and less than or equal to the second value, then the first relationship corresponding to the initial water content is:

[0146]

[0147] Wherein, λ represents the water content of the fuel cell stack;

[0148] If the initial water content is greater than the second value, then the first relationship corresponding to the initial water content is:

[0149]

[0150] Wherein, σ(m, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is m, m is the second value, σ(x, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is x, σ(xy, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is xy, x and y are coefficients obtained by fitting based on experimental measurements, and 0 < y < 1, x <m。

[0151] Optionally, the process by which the high-frequency impedance calculation subunit calculates the high-frequency impedance of the fuel cell based on the relationship between the conductivity of the proton exchange membrane and the high-frequency impedance of the fuel cell may include:

[0152] The ionic impedance of the proton exchange membrane of the fuel cell is calculated based on the relationship between the conductivity of the proton exchange membrane and the ionic impedance of the proton exchange membrane.

[0153] The ohmic impedance of the fuel cell proton conductor is calculated based on the relationship between the ionic impedance of the fuel cell proton exchange membrane and the ohmic impedance of the fuel cell proton conductor.

[0154] The calculated value of the high-frequency impedance of the fuel cell is obtained by calculating the relationship between the ohmic impedance of the proton conductor and the high-frequency impedance of the fuel cell.

[0155] Optionally, the fuel cell stack water content monitoring device may further include:

[0156] The water content determination unit is used to determine whether the initial water content is less than a third value before the high-frequency impedance calculation unit calculates the high-frequency impedance of the fuel cell based on the relationship between the initial water content, the stack temperature and the high-frequency impedance of the fuel cell.

[0157] If the initial water content is less than the third value, then the high-frequency impedance calculation unit performs a calculation based on the relationship between the initial water content, the stack temperature, and the high-frequency impedance of the fuel cell to obtain the calculated value of the high-frequency impedance of the fuel cell.

[0158] This application embodiment also provides a storage medium that can store a program suitable for execution by a processor, the program being used to implement various processing steps in the aforementioned fuel cell stack water content monitoring scheme.

[0159] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0160] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0161] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for monitoring water content in a fuel cell stack, characterized in that, include: Set the initial water content of the fuel cell stack; The high-frequency impedance of the fuel cell and the stack temperature of the fuel cell stack are obtained. The calculated value of the high-frequency impedance of the fuel cell is obtained by calculating the relationship between the initial water content, the stack temperature, and the high-frequency impedance of the fuel cell. Calculate the absolute value of the difference between the calculated value of the high-frequency impedance and the measured value of the high-frequency impedance; If the absolute value is greater than the preset error threshold, the initial water content is updated according to the preset rules until the absolute value of the difference between the calculated value of the high-frequency impedance of the fuel cell, obtained by calculating the relationship between the updated initial water content, the stack temperature and the high-frequency impedance of the fuel cell and the measured value of the high-frequency impedance is not greater than the preset error threshold. The updated initial water content is set as the reference water content for the fuel cell; The calculated value of the high-frequency impedance of the fuel cell is obtained by calculating the relationship between the initial water content, the stack temperature, and the high-frequency impedance of the fuel cell, including: Based on the initial water content, a first relationship is determined, which is the relationship between the water content of the fuel cell stack, the temperature of the fuel cell stack, and the conductivity of the proton exchange membrane of the fuel cell. The initial water content and the stack temperature are substituted into the first relationship to calculate the proton exchange membrane conductivity of the fuel cell. The calculated value of the high-frequency impedance of the fuel cell is obtained by calculating the relationship between the conductivity of the proton exchange membrane and the high-frequency impedance of the fuel cell. The process of determining the first relationship corresponding to the initial water content based on the initial water content includes: If the initial water content is less than the first value, then the first relationship corresponding to the initial water content is: ； Where σ is the proton exchange membrane conductivity of the fuel cell, p is the first value, T is the fuel cell stack temperature, k is the temperature conversion coefficient, and a, b, c, and n are coefficients obtained by fitting through experimental measurements. If the initial water content is greater than or equal to the first value and less than or equal to the second value, then the first relationship corresponding to the initial water content is: ； Wherein, λ represents the water content of the fuel cell stack; If the initial water content is greater than the second value, then the first relationship corresponding to the initial water content is: ； Wherein, σ(m, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is m, m is the second value, σ(x, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is x, σ(xy, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is xy, x and y are coefficients obtained by fitting based on experimental measurements, and 0 < y < 1, x <m。 2. The method according to claim 1, characterized in that, The high-frequency impedance of the fuel cell is calculated based on the relationship between the proton exchange membrane conductivity and the high-frequency impedance of the fuel cell, including: The ionic impedance of the proton exchange membrane of the fuel cell is calculated based on the relationship between the conductivity of the proton exchange membrane and the ionic impedance of the proton exchange membrane. The ohmic impedance of the fuel cell proton conductor is calculated based on the relationship between the ionic impedance of the fuel cell proton exchange membrane and the ohmic impedance of the fuel cell proton conductor. The calculated value of the high-frequency impedance of the fuel cell is obtained by calculating the relationship between the ohmic impedance of the proton conductor and the high-frequency impedance of the fuel cell.

3. The method according to claim 1 or 2, characterized in that, Before calculating the high-frequency impedance of the fuel cell based on the relationship between the initial water content, the stack temperature, and the high-frequency impedance of the fuel cell, the process further includes: Determine whether the initial water content is less than the third value; If the initial water content is less than the third value, then the step of calculating the high-frequency impedance of the fuel cell based on the relationship between the initial water content, the stack temperature, and the high-frequency impedance of the fuel cell is performed.

4. A device for monitoring the water content of a fuel cell stack, characterized in that, include: A water content setting unit is used to set the initial water content of the fuel cell stack; The measurement acquisition unit is used to acquire the measured value of the high-frequency impedance of the fuel cell and the stack temperature of the fuel cell stack; A high-frequency impedance calculation unit is used to calculate the high-frequency impedance of the fuel cell based on the relationship between the initial water content, the stack temperature and the high-frequency impedance of the fuel cell. An error calculation unit is used to calculate the absolute value of the difference between the calculated value of the high-frequency impedance and the measured value of the high-frequency impedance. If the absolute value is greater than a preset error threshold, then the following steps of the water content update unit are executed; if the absolute value is not greater than the preset error threshold, then the following steps of the reference water content setting unit are executed. A water content update unit is used to update the initial water content according to a preset rule and return to the step of executing the high-frequency impedance calculation unit; A reference water content setting unit is used to set the updated initial water content as the reference water content of the fuel cell; The high-frequency impedance calculation unit calculates the high-frequency impedance of the fuel cell based on the relationship between the initial water content, the stack temperature, and the high-frequency impedance of the fuel cell, including: Based on the initial water content, a first relationship is determined, which is the relationship between the water content of the fuel cell stack, the temperature of the fuel cell stack, and the conductivity of the proton exchange membrane of the fuel cell. The initial water content and the stack temperature are substituted into the first relationship to calculate the proton exchange membrane conductivity of the fuel cell. The calculated value of the high-frequency impedance of the fuel cell is obtained by calculating the relationship between the conductivity of the proton exchange membrane and the high-frequency impedance of the fuel cell. The process of determining the first relationship corresponding to the initial water content based on the initial water content includes: If the initial water content is less than the first value, then the first relationship corresponding to the initial water content is: ； Where σ is the proton exchange membrane conductivity of the fuel cell, p is the first value, T is the fuel cell stack temperature, k is the temperature conversion coefficient, and a, b, c, ..., n are coefficients obtained by fitting through experimental measurement. If the initial water content is greater than or equal to the first value and less than or equal to the second value, then the first relationship corresponding to the initial water content is: ； Wherein, λ represents the water content of the fuel cell stack; If the initial water content is greater than the second value, then the first relationship corresponding to the initial water content is: ； Wherein, σ(m, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is m, m is the second value, σ(x, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is x, σ(xy, T) is the proton exchange membrane conductivity of the fuel cell calculated when the initial water content is xy, x and y are coefficients obtained by fitting based on experimental measurements, and 0 < y < 1, x <m。 5. A water content monitoring system for a fuel cell stack, characterized in that, include: DC-DC converters and fuel cell controllers; The DC-DC voltage converter includes: a digital signal processor, a current sensor, and a signal conditioning circuit; The fuel cell controller includes: an analog-to-digital converter and a microcontroller; The digital signal processor is used to superimpose an excitation current at the output terminal of the fuel cell stack. The current sensor is used to measure the bus current at the output terminal of the fuel cell stack and transmit the bus current to the signal conditioning circuit. The signal conditioning circuit is used to measure the bus voltage at the output terminal of the fuel cell stack, modulate the bus voltage and the bus current, and input the modulated bus current and the modulated bus voltage into the analog-to-digital converter. The analog-to-digital converter is used to sample the modulated bus current and the modulated bus voltage respectively to obtain sampled current and sampled voltage, extract the target current and target voltage in the target frequency domain, and transmit the target current and target voltage to the microcontroller. The microcontroller is used to calculate the measured value of the high-frequency impedance of the fuel cell based on the target current and the target voltage, and to execute each step of the fuel cell stack water content monitoring method according to any one of claims 1-3.

6. A storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements each step of the fuel cell stack water content monitoring method as described in any one of claims 1-3.

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