Method for improving monomer voltage consistency based on monomer voltage partition detection

Abstract

The invention discloses a method for improving monomer voltage consistency based on monomer voltage partition detection, and belongs to the technical field of proton exchange membrane fuel cells. Different operation parameters are adjusted according to different difference conditions to improve the consistency in time by comparing the mutual differences of the single voltages of different partitions, so that the consistency deterioration is avoided, and the service life of the galvanic pile is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of proton exchange membrane fuel cells, and in particular relates to a method for improving the consistency of single cell voltage based on single cell voltage partition detection. Background Art

[0002] Proton Exchange Membrane Fuel Cell (PEM fuel cell), as an advanced energy conversion device, has the core advantage of being able to directly convert hydrogen and oxygen into electrical energy through electrochemical reactions. This process is not only efficient but also environmentally friendly, only produces water as a byproduct, and has no greenhouse gas or other harmful substances emitted. It is an important technical path to achieve green energy transformation. PEM fuel cell technology not only shows great potential in the field of transportation (such as electric vehicles, buses and hydrogen trains), but is also increasingly valued in distributed power generation, backup power and fixed energy supply systems, becoming a key force in promoting the transformation of a green and low-carbon economy.

[0003] As the core component of the entire system, the PEMFC stack is composed of multiple cells connected in series. Its performance and life are directly affected by the consistency of the cells. The slight performance differences between cells will gradually accumulate during long-term operation, causing some cells to decay prematurely, becoming a decisive factor in the life of the entire stack. Therefore, ensuring the high consistency between the cells inside the stack is the key to extending the service life of the PEMFC stack and improving system reliability and economy.

[0004] Currently, single cell voltage detection systems are generally integrated inside the battery stack as the first line of defense to monitor battery status and prevent failures. However, traditional monitoring strategies mainly focus on setting the minimum protection threshold of single cell voltage. Once it is detected that the voltage of a single cell is lower than this threshold, measures such as load reduction or emergency shutdown are taken to avoid further damage to the battery. Although this "one-size-fits-all" protection mechanism can effectively prevent battery failure in extreme cases, it lacks refined management of single cell performance differences and cannot dynamically adjust operating parameters according to the actual distribution of single cell voltages to optimize voltage consistency. As a result, it is impossible to fundamentally slow down the battery attenuation rate, resulting in a premature decline in the overall performance of the battery stack.

[0005] In addition, the water balance state inside the PEMFC stack is another key factor affecting the stability and life of the system. During the electrochemical reaction, the generation and consumption of water are in dynamic balance. Once this balance is broken, such as membrane drying or flooding, it will have an adverse effect on the performance of the battery, and even cause permanent damage in severe cases. Most existing fuel cell systems use fixed operating conditions and lack the ability to monitor and actively regulate changes in the water balance state in real time, which makes it easy for the water balance of the stack to continue to shift in an unfavorable direction, accelerating the degradation of performance.

[0006] In summary, although PEMFC technology has shown great potential in the energy field, the maintenance of the consistency of single cells in the stack and the precise management of the water balance state are still technical bottlenecks that restrict its widespread application and long-term performance optimization. Therefore, the development of a PEMFC management system that can monitor the voltage distribution of single cells in real time, intelligently adjust operating parameters to improve voltage consistency, and has the ability to dynamically identify and actively regulate the water balance state is of great significance for improving the overall performance of PEMFC stacks, extending their service life, and promoting the commercialization of PEMFC technology. Summary of the invention

[0007] In view of the deficiencies in the prior art, the present invention provides a method for improving cell voltage consistency based on cell voltage partition detection. By comparing the differences in cell voltages in different partitions, different operating parameters are adjusted according to different differences to timely improve consistency and avoid consistency deterioration, thereby extending the life of the battery stack.

[0008] The specific technical solutions of the present invention are as follows: A method for improving cell voltage consistency based on cell voltage partition detection, the PEM fuel cell includes a stack, the stack is composed of a plurality of cells, the stack also includes an air inlet and an air outlet, and the air inlet and the air outlet are at the same end of the stack, comprising: (1) Starting from the end of the stack with the air inlet and outlet, the single cells in the PEM fuel cell stack are divided into three regions: front end, middle end and rear end according to the end plate effect; (2) Calculate the average voltage of each cell in each region, which are defined as before Ave, during Ave, and after Ave; (3) Operate the stack at constant current for at least 10 minutes; (4) Compare before Ave, during Ave and Ave: (4.1) When Ave before>Ave in>Ave after, and the difference between Ave before and Ave after exceeds a preset threshold, the measure taken is to increase the air metering ratio; Since the air intake of each single piece decreases from front to back, if Ave front>Ave middle>Ave back, and the difference between Ave front and Ave back exceeds the preset threshold, it means that the air intake of the rear part is insufficient and the metering ratio needs to be increased; (4.2) When both Ave before and Ave after are smaller than Ave in the middle, and the difference between Ave in the middle and the smaller of Ave before and Ave after exceeds a preset threshold, the measure to be taken is to simultaneously increase the water inlet temperature and the water outlet temperature, and keep the temperature difference between the water inlet temperature and the water outlet temperature unchanged, and not exceed the maximum allowable temperature of the fuel cell stack during operation; There is an end plate effect on the front and rear plates, that is, the temperature is relatively low relative to the middle, and the temperature has a key impact on the drainage of the battery stack. Low temperature will cause relatively poor drainage. Therefore, if Ave before and Ave after are both smaller than Ave in the middle, and the difference between Ave in the middle and the smaller of Ave before and Ave after exceeds the preset threshold and lasts for 1 minute, it means that the drainage of the front and rear single cells is not smooth, causing the diffusion layer, porous layer, and catalyst layer inlet holes to be blocked, and the mass transfer resistance to increase, thereby reducing performance; (4.3) When both Ave before and Ave after are greater than Ave in, and the difference between the smaller of Ave before and Ave after and Ave in exceeds a preset threshold, the measure taken is to simultaneously reduce the water inlet temperature and the water outlet temperature, and keep the temperature difference between the water inlet temperature and the water outlet temperature unchanged; There is an end plate effect in the front and rear sheets, that is, the temperature is relatively low relative to the middle, and the temperature has a key influence on the drainage of the battery stack. Low temperature will cause relatively poor drainage. Therefore, if Ave before and Ave after are both greater than Ave in the middle, and the difference between the smaller of Ave before and Ave after and Ave in the middle exceeds the preset threshold, and lasts for 1 minute, it means that the temperature of the middle single cell is too high and is always in a state of dehydration. Water is the key carrier of proton transport in the ionomer in the catalyst layer and the membrane. Dehydration causes an increase in proton transport resistance, that is, an increase in ohmic resistance, which causes performance degradation. A dry membrane will not only cause low performance, but if it continues to be dry, it will cause continuous shrinkage of the membrane, produce micro cracks, and even produce local hot spots to cause membrane perforation, resulting in single-chip failure. Take measures to reduce drainage performance, keep moisture inside the single cell, and improve proton transport capacity.

[0009] The preset threshold is pre-set according to the characteristics and operating conditions of the PEM fuel cell stack and is used to determine whether the water balance state inside the stack has deteriorated.

[0010] Preferably, in step (1), the number of single cells in the front, middle and rear regions is 3 to 5 respectively.

[0011] In some embodiments of the present invention, for example: the air inlet and outlet ends are defined as the front end, and the 5 sheets at the two ends are the 5 sheets that are obviously affected by the end plate effect (uneven temperature and uneven air intake), so the average values ​​of the 5 sheets at the front, middle and rear are selected in this patent as the judgment data for the deviation. The average voltage value of the 5 sheets at the front end is defined as Ave front, the average voltage value of the 5 sheets in the middle is defined as Ave middle, and the average voltage value of the 5 sheets at the rear is defined as Ave rear. According to the operating characteristics of the battery stack, the temperature at the front and rear ends is lower than that in the middle, and the temperature has a significant effect on the drainage of the battery stack. If the battery stack is flooded, it will cause air intake compensation, resulting in low performance. The flooding situation of each area of ​​the battery stack can be judged by comparing the average voltage difference between the front, rear and middle. The air intake volume at the front, middle and rear gradually decreases. By comparing the difference in the single cell voltage in the front, middle and rear areas, the deviation of the air intake volume can be judged.

[0012] The present invention can utilize the existing CVM single-cell voltage monitoring system to perform voltage detection and data analysis without the need for additional hardware configuration.

[0013] Preferably, in step (3), the stack is operated under constant current conditions for 10 to 20 minutes, and the specific parameters can be determined according to the results of the stack sensitivity test.

[0014] Preferably, in step (4), the comparison between before Ave, during Ave and at Ave lasts for at least 1 minute to eliminate the influence of polarization fluctuations during load variation.

[0015] Preferably, in step (4.1), the air stoichiometric ratio is increased by 5% to 20%. The tail air intake is insufficient and the air stoichiometric ratio needs to be increased. The air stoichiometric ratio can be selected between 5% and 20%. The specific parameters can be determined according to the results of the stack sensitivity test. In the embodiment of the present invention, 10% to 15% is selected.

[0016] Preferably, in step (4.2), the water inlet temperature and the water outlet temperature are simultaneously increased by at least 3°C, and the specific parameters can be determined according to the results of the stack sensitivity test; if the increased water inlet temperature and the water outlet temperature exceed the maximum allowable temperature during the operation of the stack, the maximum allowable temperature during the operation of the stack is used.

[0017] Preferably, in step (4.3), both the water inlet temperature and the water outlet temperature are reduced by at least 3°C. The specific parameters can be determined according to the results of the stack sensitivity test.

[0018] Preferably, in step (4), the measures taken are run for 5 to 15 minutes, and the specific parameters can be determined according to the results of the stack sensitivity test.

[0019] Furthermore, because the water balance inside the fuel cell stack is always in dynamic change, the operating conditions are adjusted according to the above three situations. If it continues, it may cause the water balance to deteriorate in the opposite direction. Therefore, after the measures are taken, the fuel cell stack is restored to the original operating conditions for 5 minutes, and then Ave before, Ave during and Ave are compared again. If the single cell voltages are inconsistent, measures are taken again to adjust the operating parameters through steps (4.1) to (4.3) according to the comparison results.

[0020] That is, after adjusting the operating parameters, the cell voltage changes of the fuel cell stack are continuously monitored, and the operating parameters are further adjusted as needed to maintain the water balance state inside the fuel cell stack, thereby ensuring the consistency of the cell voltage.

[0021] Beneficial effects of the present invention: The present invention determines the water balance state inside the fuel cell stack according to the relative difference in the voltage of the cells at the front, middle and rear of the fuel cell stack, and designs corresponding measures to improve the water balance in time, thereby avoiding excessive attenuation caused by continuous deterioration of the water balance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of a method for improving cell voltage consistency based on cell voltage partition detection according to the present invention.

[0023] Figure 2 This is a diagram showing the change in air stoichiometric ratio in Example 1.

[0024] Figure 3 The voltage variation trend of the cells in the front, middle and rear partitions in Example 1 is shown.

[0025] Figure 4 This is the changing trend of water inlet and outlet temperatures in Example 3.

[0026] Figure 5 The voltage variation trend of the cells in the front, middle and rear partitions in Example 3 is shown. DETAILED DESCRIPTION

[0027] Example 1 In the fuel cell system, when the electric density point is set to 0.5 A / cm², the stack consists of 400 cells, and the effective reaction area of ​​each cell is 360 cm². In order to ensure the stability of the water balance inside the stack, the system first runs at constant current for 10 minutes. Subsequently, the average voltages of the first 5 cells (first 5ave), the middle 5 cells (middle 5ave), and the last 5 cells (last 5ave) are compared and analyzed.

[0028] During operation, it was monitored that the average voltage of the front group of single cells was higher than that of the middle group, which was higher than that of the rear group. The voltage difference between the front and rear groups exceeded 25mV and lasted for 1 minute.

[0029] according to Figure 1 The control strategy in the system determines that the tail air intake is insufficient, resulting in uneven voltage distribution. Therefore, the system immediately takes measures to increase the air metering ratio by 10% to 2.2 ( Figure 2 ), and continued to run for 10 minutes. With the increase of the metering ratio, the average voltages at the front, middle and rear all increased ( Figure 3 ). However, there is no air shortage problem in the front and middle positions, so the voltage increases less. There is an air shortage problem in the rear, so the voltage increases significantly, which improves the average voltage difference between the front and rear to within the threshold.

[0030] After the measures were implemented, the average voltage of the front, middle and rear groups of cells was measured again. Figure 3 It shows that the voltage of the front group is still higher than that of the middle group, and the middle group is higher than that of the rear group, but the voltage difference between the groups has been significantly reduced, all within 10mV. This shows that increasing the air stoichiometric ratio effectively improves the problem of uneven voltage distribution and improves the overall performance of the stack.

[0031] Example 2

[0032] In the fuel cell system, when the electric density point is set to 1.2 A / cm², the stack consists of 400 cells, and the effective reaction area of ​​each cell is 360 cm². In order to ensure the stability of the water balance inside the stack, the system first runs at constant current for 10 minutes. Subsequently, the average voltages of the first 5 cells (first 5ave), the middle 5 cells (middle 5ave), and the last 5 cells (last 5ave) are compared and analyzed.

[0033] During operation, it was monitored that the average voltage of the single cells in the middle group was higher than those in the front and rear groups, and the difference between the middle group and the lower voltage in the front or rear group exceeded 25mV and lasted for 1 minute.

[0034] according to Figure 1 The control strategy in the system determines that the front and rear cells are not draining well, which may be due to the low temperature, resulting in a decrease in drainage performance. Therefore, the system takes measures to simultaneously increase the water inlet and outlet temperatures by 3°C (keeping the water inlet and outlet temperature difference unchanged) and ensures that the maximum allowable temperature is not exceeded, and continues to run for 10 minutes.

[0035] After the measures were implemented, the voltage was measured again, and it was found that the average voltage difference of the front, middle and rear groups of cells was significantly reduced, all within 10mV. This shows that the optimization measures of increasing water temperature and drainage performance have effectively improved the voltage distribution and enhanced the drainage performance and overall performance of the battery stack.

[0036] Example 3

[0037] In the fuel cell system, when the electric density point is set to 1.6 A / cm², the stack consists of 400 cells, and the effective reaction area of ​​each cell is 360 cm². In order to ensure the stability of the water balance inside the stack, the system first runs at constant current for 10 minutes. Subsequently, the average voltages of the first 5 cells (first 5ave), the middle 5 cells (middle 5ave), and the last 5 cells (last 5ave) are compared and analyzed.

[0038] After running under constant current conditions, it was monitored that the average voltage of the single cells in the front and rear groups were higher than that in the middle group, and the difference between the higher voltage in the front or rear group and the middle group exceeded 25mV and lasted for 1 minute.

[0039] according to Figure 1 The control strategy determines that the temperature of the middle single cell is too high and is in a water loss state. Therefore, the system takes measures to reduce the water inlet and outlet temperatures by 3°C around 300s (keeping the water inlet and outlet temperature difference unchanged) ( Figure 4 ) for 10 minutes to reduce the drainage performance and keep the moisture inside the single cell.

[0040] From the perspective of catalyst activity, lowering the temperature will also reduce the catalyst activity. However, as the temperature decreases, the average voltage of the front, middle and rear 5 sheets increases at the same time, indicating that the membrane electrode is indeed dry. Therefore, the temperature decreases, reducing the drainage effect, improving the dryness, and thus improving the performance. Due to the end plate effect, the temperature of the front and rear sheets is lower than that of the middle sheet, so the dryness is relatively milder than that of the middle sheet, and the voltage increases by about 5mV. The temperature of the middle sheet is high and the dryness is serious. Therefore, the dryness is significantly improved after the temperature is lowered, so the performance is significantly improved, and the voltage increases by about 22mV ( Figure 5 ). Therefore, the difference between the front, back and middle pieces is reduced to within the threshold value of 25mV.

[0041] After the measures were implemented, the voltage was measured again, and it was found that the average voltage difference of the front, middle and rear groups of single cells was significantly reduced, all within 10mV. This shows that the measures of lowering the water temperature and improving the moisturizing performance have effectively improved the problem of uneven voltage distribution and improved the proton transmission capacity and overall performance of the battery stack.

Claims

1. A method for improving cell voltage consistency based on cell voltage partition detection, wherein the PEM fuel cell comprises a stack, the stack is composed of a plurality of cells, the stack further comprises an air inlet and an air outlet, and the air inlet and the air outlet are at the same end of the stack, characterized in that: include: (1) Starting from the end of the stack with the air inlet and outlet, the single cells in the PEM fuel cell stack are divided into three regions: front end, middle end and rear end according to the end plate effect; (2) Calculate the average voltage of each cell in each region, which are defined as before Ave, during Ave, and after Ave; (3) Operate the stack at constant current for at least 10 minutes; (4) Compare before Ave, during Ave and Ave: (4.1) When Ave before>Ave in>Ave after, and the difference between Ave before and Ave after exceeds a preset threshold, the measure taken is to increase the air metering ratio; (4.2) When both Ave before and Ave after are smaller than Ave in the middle, and the difference between Ave in the middle and the smaller of Ave before and Ave after exceeds a preset threshold, the measure to be taken is to simultaneously increase the water inlet temperature and the water outlet temperature, and keep the temperature difference between the water inlet temperature and the water outlet temperature unchanged, and not exceed the maximum allowable temperature of the fuel cell stack during operation; (4.3) When both Ave before and Ave after are greater than Ave in, and the difference between the smaller of Ave before and Ave after and Ave in exceeds a preset threshold, the measure taken is to simultaneously reduce the water inlet temperature and the water outlet temperature, and keep the temperature difference between the water inlet temperature and the water outlet temperature unchanged.

2. The method for improving cell voltage consistency based on cell voltage partition detection according to claim 1, characterized in that: In step (1), the number of single cells in the front, middle and rear regions is 3 to 5 respectively.

3. The method for improving cell voltage consistency based on cell voltage partition detection according to claim 1, characterized in that: In step (3), the stack is operated at a constant current for 10 to 20 minutes.

4. The method for improving cell voltage consistency based on cell voltage partition detection according to claim 1, characterized in that: In step (4), the comparison of before Ave, during Ave and at Ave lasts for at least 1 minute.

5. The method for improving cell voltage consistency based on cell voltage partition detection according to claim 1, characterized in that: In step (4.1), increase the air metering ratio by 5% to 20%.

6. The method for improving cell voltage consistency based on cell voltage partition detection according to claim 1, characterized in that: In step (4.2), the water inlet temperature and the water outlet temperature are increased by at least 3°C ​​at the same time; if the increased water inlet temperature and the water outlet temperature exceed the maximum allowable temperature of the fuel cell stack during operation, the maximum allowable temperature of the fuel cell stack during operation is used.

7. The method for improving cell voltage consistency based on cell voltage partition detection according to claim 1, characterized in that: In step (4.3), reduce both the water inlet temperature and the water outlet temperature by at least 3°C.

8. The method for improving cell voltage consistency based on cell voltage partition detection according to claim 1, characterized in that: In step (4), the measures taken take 5 to 15 minutes to run.

9. The method for improving cell voltage consistency based on cell voltage partition detection according to claim 8, characterized in that: After the measures are taken, restore the stack to the original operating conditions and run for 5 minutes. Compare Ave before, Ave during and Ave again. If the cell voltages are inconsistent, take measures to adjust the operating parameters through steps (4.1) to (4.3) based on the comparison results.

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