Method for detecting water content of fuel cell

Abstract

The invention provides a method for detecting the water content of a fuel cell. The method comprises the following steps: measuring a voltage signal of the fuel cell; processing the measured voltage signal to extract a first-order component of the voltage fluctuation signal; and obtaining the water content of the fuel cell based on the first-order component of the extracted voltage fluctuation signal and a predetermined mapping relation between the first-order component of the voltage fluctuation signal of the fuel cell and the water content. Through the method, the water content of each single cell of the fuel cell stack can be detected at a relatively low cost.

Description

Technical Field

[0001] The present disclosure relates to the field of fuel cells, and more particularly to a method for detecting water content in a fuel cell. Background Art

[0002] Cold-start performance is crucial for the practical application of fuel cells, especially in applications such as vehicles in cold climates. Specifically, cold-start performance refers to the ability of a fuel cell to resume operation after a specified period of complete shutdown in low-temperature conditions. It has been noted that when a fuel cell is exposed to subzero temperatures for extended periods, residual moisture within the fuel cell freezes, blocking gas transmission pathways and causing cold-start failure. Furthermore, this freezing can damage the microstructure of the fuel cell electrodes, adversely affecting the fuel cell's operating life.

[0003] Therefore, to ensure robust cold-start performance, the purge process during the previous shutdown is crucial. That is, before the fuel cell system completely stops, gas continues to flow into the fuel cell to purge out any liquid water within it, preventing subsequent freezing. Furthermore, this purge process reduces the water content of the fuel cell's proton exchange membrane to an appropriate level, which is also crucial for a successful cold start.

[0004] Currently, high-frequency impedance (HFR) is commonly used as an indicator of water content during the purge process. High-frequency impedance can be measured using a DC-DC converter (DC / DC) on the vehicle. However, this DC / DC converter can only measure the high-frequency impedance of the entire fuel cell stack, so the measured high-frequency impedance can only be used to reflect the water content of the entire fuel cell stack. In reality, the water content of multiple cells in a fuel cell stack varies greatly. Figure 1 The figure shows the high frequency impedance of each cell in a fuel cell stack consisting of 20 cells when the shutdown purge is completed. Figure 1 In the example shown, the high-frequency impedance of the fuel cell stack as a whole has reached the target value. However, the high-frequency impedance of some cells, such as cells 12 and 19, is still very low, indicating that the water content in these cells is still high. Therefore, these cells may still fail during the next cold start.

[0005] In summary, a method is needed to detect the water content of each cell in a fuel cell stack. If high-frequency impedance is still used as an indicator, the high-frequency impedance of each cell must be measured. However, detecting high-frequency impedance is relatively complex, and the cost of updating both the hardware and software is high.

[0006] It is based on the above background that the method for detecting the water content of a fuel cell of the present application is proposed. Summary of the Invention

[0007] This disclosure proposes a method for detecting the water content of a fuel cell. This method can detect the water content of each cell in a fuel cell stack in real time during the purge process, thereby adjusting the purge strategy based on the real-time detected water content, such as adjusting the purge time, to ensure that the water content of each cell reaches the target value. More importantly, this method only requires obtaining the voltage signal of each cell through existing equipment and then updating the software to perform mathematical processing on the obtained voltage signal. No hardware updates are required to achieve the water content detection function. Therefore, this method can be easily applied to existing electric vehicle fuel cell systems and has a low cost of use.

[0008] Specifically, the present disclosure provides a method for detecting the water content of a fuel cell. The method includes the following steps: measuring a voltage signal of the fuel cell; processing the measured voltage signal to extract a first-order component of a voltage fluctuation signal; and obtaining the water content of the fuel cell based on the extracted first-order component of the voltage fluctuation signal and a predetermined mapping relationship between the first-order component of the fuel cell voltage fluctuation signal and the water content.

[0009] The present disclosure also provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the above method is implemented.

[0010] The present disclosure further provides a computer program product. The computer program product includes a computer program. When the computer program is executed by a processor, the above method is implemented.

[0011] In general, the various embodiments of the present disclosure may be combined and coupled in any possible manner within the scope of the present disclosure. These and other aspects, features and / or advantages of the present disclosure will be apparent and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Embodiments of the present disclosure will be described by way of example with reference to the following drawings, in which:

[0013] Figure 1 The figure shows the high-frequency impedance of each cell in a fuel cell stack including 20 cells in the prior art when the shutdown purge is completed;

[0014] Figure 2 Schematic diagram showing the mapping of high-frequency impedance of a fuel cell to water content;

[0015] Figure 3 The diagram schematically shows the relative change trend between the first-order component of the fuel cell voltage fluctuation signal and the high-frequency impedance;

[0016] Figure 4 A flow chart showing a method for detecting water content in a fuel cell according to one embodiment of the present disclosure; and

[0017] Figure 5 Shows Figure 4 The result of the voltage fluctuation signal decomposition step of the method is shown.

[0018] It should be understood that the drawings illustrate only one way of implementing the present disclosure and should not be construed as limiting other possible embodiments within the scope of the appended claims. The scope of protection of the present disclosure is limited only by the appended claims. DETAILED DESCRIPTION

[0019] The electrical resistance of a fuel cell is closely related to its water content. For this reason, the high-frequency impedance of the fuel cell stack is often used as an indicator of water content during current fuel cell stack purge processes. While the specific frequency range may vary depending on the research and application, high frequency can generally be considered to be in the range of several hundred hertz to several thousand hertz, and high-frequency impedance refers to the impedance amplitude of the fuel cell stack at that frequency. High-frequency impedance can effectively reflect the water content of the fuel cell stack's proton exchange membrane.

[0020] Figure 2 The mapping relationship between the high-frequency impedance and water content of the fuel cell is schematically shown. Whether for the fuel cell stack as a whole or for each single cell in the fuel cell stack, the high-frequency impedance and water content roughly have the mapping relationship depicted in the figure. Figure 2 It can be seen that the high-frequency impedance of the fuel cell is a monotonically decreasing function of the water content, that is, as the water content of the fuel cell gradually decreases, its high-frequency impedance gradually increases. In particular, when the water content of the fuel cell decreases to a certain range, its high-frequency impedance increases rapidly. Typically, the mapping relationship between the high-frequency impedance of the fuel cell and the water content is stored in the control unit of the fuel cell system. Subsequently, during the purge process of the fuel cell stack, the high-frequency impedance of the fuel cell stack is measured in real time (the corresponding frequency can be predetermined), and the water content value is obtained based on the measured high-frequency impedance through the above mapping relationship. Then, based on the obtained water content value, the purge strategy is adjusted, such as continuing to purge or stopping purge.

[0021] However, as described in the background section, the measured high-frequency impedance of a fuel cell stack can only reflect the average water content of the entire fuel cell stack, but cannot accurately reflect the water content of each individual cell. Furthermore, to measure the high-frequency impedance of each individual cell in real time to reflect the water content of each cell, complex hardware must be configured in the fuel cell system, which will result in high costs.

[0022] In the process of seeking a solution to the above problem, the inventors of the present application found that the water content of each cell can be obtained by using the voltage signal of the single cell of the fuel cell stack measured in real time. Specifically, the inventors of the present application found that during the purge process of the fuel cell stack, the change trend of the first-order component of the voltage fluctuation signal of each cell is basically the same as the change trend of the high-frequency impedance, such as Figure 3 As shown. Figure 3 In the figure, the horizontal axis represents time, the solid line represents the changing trend of the first-order component of the voltage fluctuation signal over time, and the dotted line represents the changing trend of the high-frequency impedance over time. As can be seen from the figure, the changing trends of the two are basically the same. In an exemplary embodiment, a simple linear multiple relationship can be established between the first-order component of the voltage fluctuation signal of a single cell and the water content. Therefore, the inventors of the present application found that the first-order component of the voltage fluctuation signal of a single cell of a fuel cell stack can be used as an indicator of the water content during the purge process, and based on this discovery, a method for detecting the water content of a fuel cell is proposed.

[0023] Figure 4 A flow chart of a method for detecting the water content of a fuel cell according to an embodiment of the present disclosure is shown. Figure 4 As shown, the method includes an offline portion on the left and an online portion on the right. The offline portion can be performed in a laboratory environment to predetermine or obtain a mapping relationship between the first-order component of the voltage fluctuation signal of a single cell of a fuel cell stack and the water content. This mapping relationship can be in the form of a curve or a lookup table. The online portion is performed during the actual application of the fuel cell stack to obtain the first-order component of the voltage fluctuation signal in real time and derive the corresponding water content based on the obtained first-order component of the voltage fluctuation signal.

[0024] The above-mentioned offline part includes steps S10-S18. When performing the offline part, the fuel cell system can be placed in a laboratory environment, and a multi-channel instrument for measuring the impedance of each single cell can be arranged on the fuel cell stack. First, in step S10, the fuel cell stack is purged, and the voltage signal and high-frequency impedance of each single cell of the fuel cell stack are measured in real time during the purging process. The voltage signal can be measured by the voltage patrol meter of the fuel cell. It will be understood that the voltage patrol meter is an existing device on the fuel cell stack, which is configured to collect the voltage signal of each single cell in the fuel cell stack and perform health status assessment, fault diagnosis and positioning based on the collected voltage signal. That is to say, in this step, there is no need to set up an additional voltage measuring device. The high-frequency impedance can be measured using a multi-channel instrument. The multi-channel instrument can be used only in a laboratory environment and does not need to be used in the subsequent online part. In one embodiment according to the present disclosure, the measured high-frequency impedance is the impedance at a frequency greater than 500 Hz.

[0025] Then, in step S12, the measured voltage signal is processed to extract the first-order component of the voltage fluctuation signal. Specifically, the voltage signal measured in step S10 is a time domain signal, and includes an original voltage signal and a voltage fluctuation signal. The "original voltage signal" here refers to a stable voltage level in the absence of external interference or changes, and the "voltage fluctuation signal" refers to any changes or fluctuations that occur on the basis of the original voltage signal, and is therefore also called a voltage noise signal. In step S12, the processing of the measured voltage signal includes removing the original voltage signal from the measured voltage signal to obtain a voltage fluctuation signal, and converting the voltage fluctuation signal from the time domain to the frequency domain to decompose it, thereby obtaining voltage fluctuation signal components corresponding to different characteristic frequencies, and in particular obtaining components of the voltage fluctuation signal corresponding to the first-order characteristic frequency, that is, the first-order component of the voltage fluctuation signal.

[0026] Figure 5 The result of step S12 is displayed. Figure 5 A total of 6 signal graphs are displayed from top to bottom.

[0027] The first figure shows the voltage signal of a single cell in the fuel cell stack measured in step S10. The second figure shows the original voltage signal, with the voltage fluctuation signal filtered out. The third figure shows the first-order component of the filtered voltage fluctuation signal. The fourth to sixth figures show the second, third, and fourth-order components of the voltage fluctuation signal, respectively. Those skilled in the art will appreciate that further higher-order components of the voltage fluctuation signal exist. However, to avoid obscuring this application, these further components are not described here. This application focuses primarily on the third figure, which depicts the first-order component of the voltage fluctuation signal. As can be seen from the figure, the first-order component of the voltage fluctuation signal gradually increases as the purge process progresses. At t = 1080 s, the purge stops, and thereafter, the first-order component gradually decreases. This trend of first increasing and then decreasing is generally consistent with the changing trend of the high-frequency impedance of the single cell during the purge process. That is, the high-frequency impedance of the single cell measured in step S10 also gradually increases as the purge process progresses, then begins to gradually decrease at t = 1080 s. The physical meaning of this is that as the purge process progresses, the water content of the proton exchange membrane of the single cell gradually decreases, causing the high-frequency impedance to increase. At t = 1080s, the purge stops. Due to water redistribution and absorption of water from the gas, the overall water content of the proton exchange membrane increases, causing the high-frequency impedance value to gradually decrease.

[0028] Any suitable signal processing method can be used to decompose the voltage fluctuation signal. The signal processing method includes Fourier transform, wavelet transform, empirical mode decomposition, variational mode decomposition and Hilbert-Huang transform (HHT) and the like. The above methods are all capable of converting the voltage fluctuation signal from the time domain to the frequency domain, thereby achieving the purpose of decomposing the voltage fluctuation signal. Among them, the inventors of the present application have found that variational mode decomposition is particularly suitable for the present application. Specifically, compared with other signal processing methods, variational mode decomposition does not require pre-definition of basis functions or wavelets, and can adaptively decompose the signal by solving variational optimization problems, automatically selecting the most appropriate decomposition level according to the characteristics of the voltage fluctuation signal, and realizing effective separation of the inherent modal components. In addition, each modal component obtained by variational mode decomposition usually has a clear physical meaning, which helps to interpret and analyze the signal in practical applications. Specifically for the present application, the first-order component of the voltage fluctuation signal obtained by variational mode decomposition is associated with the high-frequency impedance of the single battery. Specifically, the change trends of the two are basically the same, such as Figure 3 As shown.

[0029] Next, in step S14, a mapping relationship between the first-order component of the voltage fluctuation signal and the high-frequency impedance is established. As mentioned above, the first-order component of the voltage fluctuation signal of the fuel cell can be proportional to the high-frequency impedance, that is, there is a simple linear multiple relationship between the two. Then, in step S16, a mapping relationship between the high-frequency impedance of the fuel cell and the water content is obtained, such as Figure 2 As shown. The reason why it is said to be "obtained" instead of "measured" here is because the mapping relationship between the high-frequency impedance of the fuel cell and the water content is usually known and has been applied during the purge process. Therefore, no additional measurement is required in this step. Finally, in step S18, based on the mapping relationship between the first-order component of the voltage fluctuation signal and the high-frequency impedance established in step S14, and the mapping relationship between the high-frequency impedance and the water content obtained in step S16, a mapping relationship between the first-order component of the voltage fluctuation signal of the fuel cell and the water content is established. This mapping relationship can be stored in the control unit of the fuel cell system for subsequent use.

[0030] The above-mentioned offline part uses the parameter of high-frequency impedance as an intermediate bridge to indirectly obtain the mapping relationship between the first-order component of the voltage fluctuation signal of the single cell of the fuel cell stack and the water content. However, the present disclosure is not limited to this. It will be understood that the offline part of the present application can also establish a mapping relationship between the first-order component of the voltage fluctuation signal and the water content by directly measuring the voltage signal and the water content. In such an embodiment, the fuel cell stack can be purged, and then the voltage signal of each single cell can be measured by a voltage patrol meter during the purge process. At the same time, the water content of the single cell, especially its proton exchange membrane, can be measured by a microprobe method, for example, and the measurement results are analyzed and processed to directly establish a mapping relationship between the first-order component of the voltage fluctuation signal and the water content. It will also be understood that other parameters can be used as intermediate bridges.

[0031] The offline part of the method disclosed herein is described in detail above. In theory, since the physical structure of each single cell of the fuel cell stack is the same, the characteristic frequency corresponding to the first-order component of the voltage fluctuation signal extracted for each single cell should be basically the same, and the mapping relationship between the first-order component of the voltage fluctuation signal of each single cell and the water content finally established should also be basically the same. Therefore, the mapping relationship between the first-order component of the voltage fluctuation signal and the water content obtained by executing the offline part steps for one of the single cells can be applied to other single cells. However, the above-mentioned offline part can be executed separately for each single cell of the fuel cell stack, with the aim of taking into account the subtle differences between each single cell and obtaining the mapping relationship between the first-order component of the voltage fluctuation signal and the water content of each single cell. In this way, a more accurate mapping relationship database between the voltage fluctuation signal and the water content can be obtained, which helps to accurately obtain the water content of different single cells in the subsequent online part.

[0032] The online part will be described below. Figure 4 As shown, the online part includes steps S20-S24. The online part refers to the part performed in the actual application of the fuel cell (especially the purge process) for real-time detection of the water content of the fuel cell. First, in step S20, the voltage signal of each single cell of the fuel cell is measured in real time. As in step S10, in step S20, the voltage signal can be measured by the voltage patrol meter of the fuel cell stack. Then, in step S22, the measured voltage signal is processed to extract the first-order component of the voltage fluctuation signal. Step S22 can be performed in a similar way to step S12 and will not be repeated here. Finally, in step S24, based on the mapping relationship between the first-order component of the voltage fluctuation signal and the first-order component of the voltage fluctuation signal obtained in the above-mentioned offline part and the water content, the water content of each single cell of the fuel cell is obtained.

[0033] The above-mentioned online part can be performed at any stage of the actual application of the fuel cell as needed to obtain the water content of each cell of the fuel cell stack at any time. However, in a preferred embodiment, the above-mentioned online part can be performed during the shutdown and purge phase of the fuel cell stack. The reason is that, on the one hand, during the shutdown and purge process, uneven purge is likely to occur, and it is necessary to know the water content information of each cell; on the other hand, Figure 2 It can be seen that the lower the water content of the fuel cell (i.e., the drier the cell), the more sensitive the high-frequency impedance is to changes in water content. The shutdown purge process is a process in which the water content gradually decreases, and the water content detection method disclosed in this process is particularly effective. Therefore, this method can effectively detect the water content of each single cell of the fuel cell stack in real time during the purge process, thereby adjusting the purge strategy based on the real-time detected water content, such as adjusting the purge time, to ensure that the water content of each single cell reaches the target value.

[0034] It will be understood that the method for detecting the water content of a fuel cell described above can be used not only to detect the water content of each single cell of a fuel cell stack, but also to detect the water content of the fuel cell stack as a whole (if necessary). In the case where the method is used to detect the water content of the fuel cell stack as a whole, the above steps S10-S18 and S20-S24 should be adaptively modified. For example, the offline part should be used to obtain the mapping relationship between the first-order component of the voltage fluctuation signal of the fuel cell stack and the water content, and in the online part, the voltage signal of the fuel cell stack should be measured in real time to ultimately obtain the water content of the fuel cell stack.

[0035] As can be seen from the above, the method disclosed herein only requires obtaining the voltage signal of each cell using an existing device (i.e., a fuel cell stack voltage inspection instrument) and performing mathematical processing on the obtained voltage signal through software updates. No hardware updates are required to achieve water content detection. Therefore, this method can be easily applied to existing electric vehicle fuel cell systems, resulting in low cost.

[0036] Reference above Figure 4 and Figure 5 A method for detecting the water content of a fuel cell according to the present disclosure is described in detail. The present disclosure also provides a computer-readable storage medium. The computer-readable storage medium stores a computer program. When executed by a processor, the computer program implements the aforementioned method. The present disclosure further provides a computer program product. The computer program product includes the computer program. When executed by a processor, the computer program implements the aforementioned method.

[0037] Although the present disclosure has been described in conjunction with the above-mentioned specific embodiments, it should not be understood as being limited in any way to the examples set forth. The scope of the present disclosure is defined by the appended claims. In the context of the claims, the terms "comprise" or "include" do not exclude other possible elements or steps. In addition, references to "one" or "an" should not be interpreted as excluding a plurality. The use of reference symbols for elements shown in the figures in the claims should not be interpreted as limiting the scope of the present disclosure. In addition, the individual features mentioned in different claims may be advantageously combined, and the mention of these features in different claims does not exclude that the combination of these features is impossible and advantageous. In addition, the terms "first", "second", "third" and "fourth" used in the present disclosure are merely used to distinguish the relevant components and are not intended to give them any priority attributes.

Claims

1. A method for detecting the water content of a fuel cell, characterized in that: The method comprises the following steps: measuring a voltage signal of the fuel cell; processing the measured voltage signal to extract a first-order component of the voltage fluctuation signal; and The water content of the fuel cell is obtained based on the extracted first-order component of the voltage fluctuation signal and a predetermined mapping relationship between the first-order component of the voltage fluctuation signal of the fuel cell and the water content.

2. The method for detecting the water content of a fuel cell according to claim 1, wherein: Predetermining the mapping relationship between the first-order component of the voltage fluctuation signal of the fuel cell and the water content includes: Establishing a mapping relationship between a first-order component of a voltage fluctuation signal of the fuel cell and a high-frequency impedance; Obtaining a mapping relationship between the high-frequency impedance and water content of the fuel cell; and Based on the mapping relationship between the first-order component of the fuel cell voltage fluctuation signal and the high-frequency impedance and the mapping relationship between the high-frequency impedance of the fuel cell and the water content, the mapping relationship between the first-order component of the fuel cell voltage fluctuation signal and the water content is determined.

3. The method for detecting the water content of a fuel cell according to claim 2, wherein: Establishing a mapping relationship between the first-order component of the voltage fluctuation signal of the fuel cell and the high-frequency impedance includes: simultaneously measuring a voltage signal and a high-frequency impedance of the fuel cell; processing the measured voltage signal to extract a first-order component of the voltage fluctuation signal; and A mapping relationship between the first-order component of the voltage fluctuation signal of the fuel cell and the high-frequency impedance is established.

4. The method for detecting the water content of a fuel cell according to claim 1 or 3, characterized in that: Processing the measured voltage signal includes removing the original voltage signal from the measured voltage signal to obtain a voltage fluctuation signal, and decomposing the voltage fluctuation signal to obtain a first-order component of the voltage fluctuation signal.

5. The method for detecting the water content of a fuel cell according to claim 4, wherein: The voltage fluctuation signal is decomposed by using a variational mode decomposition method.

6. The method for detecting the water content of a fuel cell according to claim 2 or 3, characterized in that: The established mapping relationship between the first-order component of the voltage fluctuation signal of the fuel cell and the high-frequency impedance is a linear multiple relationship.

7. The method for detecting the water content of a fuel cell according to claim 2 or 3, characterized in that: The high frequency impedance of the fuel cell is the impedance at a frequency greater than 500 Hz.

8. The method for detecting the water content of a fuel cell according to claim 1 or 3, characterized in that: The voltage signal of the fuel cell is measured by a voltage patrol meter of the fuel cell.

9. The method for detecting the water content of a fuel cell according to claim 1, wherein: The mapping relationship between the first-order component of the voltage fluctuation signal of the fuel cell and the water content is predetermined in a laboratory environment.

10. The method for detecting the water content of a fuel cell according to claim 1, wherein: The steps of the method are performed during the actual application of the fuel cell.

11. The method for detecting the water content of a fuel cell according to claim 10, wherein: The actual application process includes a shutdown purge process.

12. The method for detecting the water content of a fuel cell according to claim 1, wherein: The fuel cell is a fuel cell stack including a plurality of single cells, and the method is performed for each of the plurality of single cells.

13. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 12 is implemented.

14. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method according to any one of claims 1 to 12 is implemented.

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