Quality monitoring method and device for fuel cell stack offline

Abstract

The invention discloses a fuel cell stack offline quality monitoring method and device, and the method comprises the steps: inserting two sets of voltage collection joints CVP (cell voltage pick-up) at the left and right sides of a fuel cell stack, and achieving the collection of two voltage signals at the two ends of each cell of the stack; at a low current density point 0.5 A / cm < 2 >, the hydrogen flow and the air flow are respectively reduced, a slight air shortage state is artificially made, a defective single battery is identified by judging the difference between two voltage signals on two sides of each battery, and whether the battery is in cathode air shortage (water flooding) or anode air shortage (water flooding) is judged. According to the quality test result, the positions of the single cell with the quality problem and the cathode and anode are locked, guidance is provided for repairing of the galvanic pile, and the device and the method are simple in operation method, high in safety, low in cost and obvious in detection effect.

Description

Technical Field

[0001] The invention relates to the field of fuel cells, and in particular to a quality monitoring device and method for off-line fuel cell stacks. Background Art

[0002] In recent years, proton exchange membrane fuel cells have developed rapidly, and the upstream and downstream of the stack have achieved rapid development. The annual output of membrane electrodes, bipolar plates, stacks and systems has increased year by year. For example, the public document with the publication number CN210866380U, the publication date of 2020-06-26, and the patent name "A proton exchange membrane fuel cell monomer and a proton exchange membrane fuel cell stack" discloses a proton exchange membrane fuel cell monomer and a proton exchange membrane fuel cell stack composed of at least two proton exchange membrane fuel cell monomers stacked in series. The proton exchange membrane fuel cell monomer includes a cathode plate, an anode plate and an MEA assembly located between the cathode plate and the anode plate, and the three are stacked and fixedly sealed; the anode plate has a plurality of raised ridges, and the portion of the MEA assembly corresponding to the ridge is a deformation portion, and the gap between the ridge and the deformation portion forms a plurality of hydrogen flow channels.

[0003] Similar off-line tests for proton exchange membrane fuel cell stacks generally include test items such as air tightness test, insulation test, stack activation and polarization. The above test items can confirm the initial state of the stack from the most basic safety application perspective to ensure that the fuel cell stack achieves the most basic functions on the fuel cell engine system. During the activation and polarization process of the stack, some basic quality problems can be detected, such as low overall performance, poor consistency or low single-cell conditions. However, since the voltage inspection module CVM (cell voltage monitor) is only inserted on one side during the off-line process of the general fuel cell stack, this will result in the presence of potential (or plane current) in the plane of a certain battery. Conventional off-line inspection cannot identify such quality problems. If the stack is applied to the fuel cell engine system, the battery will heat up severely and gradually produce a single low effect, which will become the short board of the stack and affect the service life of the stack.

[0004] Therefore, for the off-line testing of fuel cell stacks, additional quality inspection methods are needed to achieve more comprehensive quality monitoring and ensure the smooth and safe application of subsequent stacks. Summary of the invention

[0005] The technical problem to be solved by the present invention is to realize a more reasonable and reliable off-line test of a fuel cell stack, determine whether there are quality problems during the production of the stack, diagnose the location of the problematic single-chip battery, and provide a basis for stack repair.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a quality monitoring method for a fuel cell stack offline, comprising the following steps:

[0007] 1) The fuel cell stack test bench is connected to the stack to be tested;

[0008] 2) The fuel cell stack test bench continues to operate at normal flow rate for the set time;

[0009] 3) The flow rate of hydrogen at the anode of the stack is supplied by first reducing and then restoring, and the flow rate of air at the anode of the stack is supplied by first reducing and then restoring;

[0010] 4) Obtain the voltage between the bipolar plates of a single cell of the battery stack.

[0011] In the step 1), the fuel cell test bench obtains voltage signals on the left and right sides of each battery in the fuel cell stack in real time.

[0012] In step 2), the load is pulled to 0.5A / cm on the fuel cell stack test bench. 2 At the current density point, run at normal flow rate for 5 minutes.

[0013] In the step 3), the flow rate of the anode hydrogen is first reduced from the flow rate corresponding to the original stoichiometric ratio of 1.5 to the flow rate corresponding to 1.2, and the process is continued for 3 minutes. Then the flow rate of the anode hydrogen is restored, and the flow rate of the air is reduced from the flow rate corresponding to the original stoichiometric ratio of 1.8 to the flow rate corresponding to 1.4, and the process is continued for 3 minutes.

[0014] In step 4), it is determined whether the absolute value of the voltage difference between the left and right sides of each battery in the battery stack is greater than a set threshold value A. If not, there is no abnormality in the battery.

[0015] In the step 4), the single-chip voltage signal collected by the CVM on the hydrogen inlet side is named U1, and the average voltage is named Umean1; the single-chip voltage signal collected by the CVM on the hydrogen outlet side is named U2, and the average voltage is named Umean2; the difference between the left and right sides of each battery in the stack is the difference between U1 and U2, and the set threshold A is 10mV.

[0016] In the step 4), if the absolute value of the difference between the left and right sides of each battery in the stack is greater than the set threshold B, it is determined whether the absolute value of the difference between U1 and Umean1 is greater than the set threshold B. If so, the cathode of the battery is under-gassing. The set threshold B is 30mV.

[0017] In the step 4), if the absolute value of the difference between the left and right sides of each battery in the stack is greater than the set threshold C, it is determined whether the absolute value of the difference between U2 and Umean2 is greater than the set threshold C. If so, the anode of the battery is under-gassing, and the set threshold C is 30mV.

[0018] A quality monitoring device for executing the quality monitoring method, characterized in that: the device is provided with a voltage acquisition connector connected to both sides of the bipolar plates of a single cell of a battery stack, the voltage acquisition connector is connected via a communication line and outputs a voltage signal to a voltage monitoring unit, the voltage monitoring unit is connected and outputs a voltage signal to a fuel cell test bench, and the fuel cell test bench displays the collected voltage signal.

[0019] Voltage collection connectors are inserted on both sides of each single-cell bipolar plate of the fuel cell stack, and each of the voltage collection connectors is connected to the voltage monitoring unit through CVP and CVM communication lines. The fuel cell test bench displays the voltage signals measured on the left and right sides of each battery in real time.

[0020] The present invention inserts two sets of voltage collection connectors CVP (cell voltage pickup) on the left and right sides of the fuel cell stack to collect two voltage signals at both ends of each battery in the stack. 2 , respectively reduce the flow of hydrogen and air, artificially create a slight lack of gas state, and identify the problematic single-chip battery by judging the difference between the two voltage signals on both sides of each battery, and judge whether the battery is lack of gas (flooding) at the cathode or anode. According to the quality test results, the single-chip battery with quality problems and the location of the anode and cathode are locked, and guidance is provided for the repair of the battery stack. The device and method are simple to operate, highly safe, low cost, and have obvious detection effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The following is a brief description of the contents expressed in each figure in the specification of the present invention and the marks in the figure:

[0022] Figure 1 A schematic diagram of a quality monitoring device and method for a fuel cell stack off-line;

[0023] Figure 2 , 3 This is a schematic diagram of the test principle;

[0024] The markings in the above figures are: 1. Fuel cell stack; 2. Voltage acquisition connector; 3. Communication line; 4. Voltage monitoring unit; 5. Fuel cell test bench. DETAILED DESCRIPTION

[0025] The following is a further detailed description of the specific implementation methods of the present invention, such as the shape, structure, relative position and connection relationship between the various components involved, the function and working principle of each part, the manufacturing process and operation method, etc., through the description of the embodiments with reference to the accompanying drawings, so as to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0026] Quality monitoring devices such as Figure 1 As shown, two sets of voltage acquisition connectors 2CVP (cell voltage pickup) are inserted on the left and right sides of the fuel cell stack 1 to collect two voltage signals at both ends of each battery in the stack 1. Voltage acquisition connectors 2 are inserted on both sides of each single cell bipolar plate of the fuel cell stack 1. Each voltage acquisition connector 2 is connected to a voltage monitoring unit 4 through CVP and CVM communication lines 3. The voltage acquisition connector 2 is connected and outputs a voltage signal to the voltage monitoring unit 4 through the communication line 3. The voltage monitoring unit 4 is connected and outputs a voltage signal to a fuel cell test bench 5. The fuel cell test bench 5 is generally composed of a processor and a display. The fuel cell test bench 5 displays the collected voltage signal, which can not only visually observe the test results, but also directly display the judgment results by comparing with the set threshold.

[0027] The fuel cell stack 1 is composed of a current collecting plate, a metal bipolar plate, a membrane electrode, an insulating plate and an end plate. Both sides of each single cell bipolar plate on the fuel cell stack 1 are plugged with a voltage collection connector 2CVP. The collected voltage signal is transmitted to the voltage monitoring unit 4CVM through a communication line 3. There are two independent voltage monitoring modules in the CVM, which are connected to the fuel cell test bench 5 through a wiring harness. The fuel cell test bench 5 can display and monitor the voltage signals measured on the left and right sides of each cell in real time. When working, the load is pulled to 0.5A / cm on the fuel cell stack 1 test bench. 2 At the current density point, the system continued to operate for 5 minutes at normal flow rate. First, the flow rate of anode hydrogen was reduced from the flow rate corresponding to the original stoichiometric ratio of 1.5 to the flow rate corresponding to 1.2, and the system was operated for 3 minutes. Then, the flow rate of anode hydrogen was restored, and the air flow rate was reduced from the flow rate corresponding to the original stoichiometric ratio of 1.8 to the flow rate corresponding to 1.4, and the system was operated for 3 minutes. The voltage signals at both ends of each battery in the stack 1 were collected.

[0028] The single-chip voltage signal collected by the CVM on the hydrogen inlet side is named U1, and the average voltage is named Umean1. The single-chip voltage signal collected by the CVM on the hydrogen outlet side is named U2, and the average voltage is named Umean2.

[0029] First, compare whether there is any difference in the voltage signals collected by the CVM on the hydrogen inlet and outlet sides. Subtract the battery voltage U1 on the hydrogen inlet side from the battery voltage U2 on the hydrogen outlet side to determine whether the absolute value of the difference is greater than 10mV. If it is less than 10mV, there is no abnormality in the battery. If it is greater than 10mV, proceed to the second step of judgment.

[0030] The second step is to compare U1 and Umean1 on the hydrogen inlet side, and U2 and Umean2 on the hydrogen outlet side. If the absolute value of the difference between U1 and Umean1 is greater than 30mV, it can be determined that the cathode of the battery is under-gased (cathode flooded); if the absolute value of the difference between U2 and Umean2 is greater than 30mV, it can be determined that the anode of the battery is under-gased (anode flooded).

[0031] Test principle:

[0032] If there are defects on the raw material bipolar plates used in the assembly of the battery stack 1 or the press-fitting process is improper, the discharge of liquid water and gas flow inside the battery will be affected. This will cause uneven current density distribution inside the battery and the presence of in-plane current inside the battery. As the use time increases, both of these situations will accelerate the attenuation of the battery and greatly reduce the service life of the entire battery stack 1.

[0033] By using a low stoichiometric ratio of reaction gas at a low current density point, the sensitivity of the single-chip battery with quality problems to the reaction gas flow rate is amplified, which is directly reflected in the voltage value on both sides of the battery. From microscopic defects, the reaction is converted into intuitive physical quantities, and the location of the quality problem is quickly and accurately identified.

[0034] like Figure 2 As shown in the figure, if the voltage difference of the same battery on the hydrogen inlet side and the hydrogen outlet side exceeds the limit and the voltage of the battery on the hydrogen inlet side also exceeds the difference with the average voltage, it means that the hydrogen inlet side of the battery is under-gased (flooded), and the location of under-gased (flooded) is at the cathode, because the accumulation of water is in the direction of gas flow (not at the anode because once flooding occurs at the anode inlet, the voltages on the hydrogen inlet and outlet sides are very low and there will be no large voltage difference). Due to the large difference in the local current density distribution inside the battery, the voltages on both sides will have a large deviation.

[0035] like Figure 3As shown in the figure, if the voltage difference of the same battery on the hydrogen inlet side and the hydrogen outlet side exceeds the limit and the voltage of the battery on the hydrogen outlet side also exceeds the difference with the average voltage, it means that the hydrogen outlet side of the battery is under-gased (flooded), and the location of under-gased (flooded) is at the anode, and the reason is that water accumulates in the direction of gas flow (not at the cathode because once flooding occurs at the cathode entrance, the voltages on the hydrogen inlet and outlet sides are very low and there will be no large voltage difference). Due to the large difference in the local current density distribution inside the battery, the voltages on both sides will have a large deviation.

[0036] The present invention is described above by way of example in conjunction with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for monitoring the quality of a fuel cell stack off-line. It is characterized in that The following steps are involved: 1) The fuel cell stack test bench is connected to the stack to be tested; 2) The fuel cell stack test bench continues to operate at normal flow rate for the set time; 3) The flow rate of hydrogen at the anode of the stack is supplied by first reducing and then restoring, and the flow rate of air at the anode of the stack is supplied by first reducing and then restoring; 4) Obtain the voltage between the bipolar plates of a single cell of the battery stack.

2. The fuel cell stack offline quality monitoring method according to claim 1, Features: In the step 1), the fuel cell test bench obtains voltage signals on the left and right sides of each battery in the fuel cell stack in real time.

3. The fuel cell stack offline quality monitoring method according to claim 1, Features: In step 2), the load is pulled to 0.5A / cm on the fuel cell stack test bench. 2 At the current density point, run at normal flow rate for 5 minutes.

4. The fuel cell stack offline quality monitoring method according to claim 1, Features: In the step 3), the flow rate of the anode hydrogen is first reduced from the flow rate corresponding to the original stoichiometric ratio of 1.5 to the flow rate corresponding to 1.2, and the process is continued for 3 minutes. Then the flow rate of the anode hydrogen is restored, and the flow rate of the air is reduced from the flow rate corresponding to the original stoichiometric ratio of 1.8 to the flow rate corresponding to 1.4, and the process is continued for 3 minutes.

5. The fuel cell stack offline quality monitoring method according to claim 1, Features: In step 4), it is determined whether the absolute value of the voltage difference between the left and right sides of each battery in the battery stack is greater than a set threshold value A. If not, there is no abnormality in the battery.

6. The fuel cell stack offline quality monitoring method according to claim 5, Features: In the step 4), the single-chip voltage signal collected by the CVM on the hydrogen inlet side is named U1, and the average voltage is named Umean1; the single-chip voltage signal collected by the CVM on the hydrogen outlet side is named U2, and the average voltage is named Umean2; the difference between the left and right sides of each battery in the stack is the difference between U1 and U2, and the set threshold A is 10mV.

7. The fuel cell stack offline quality monitoring method according to claim 6, Features: In the step 4), if the absolute value of the difference between the left and right sides of each battery in the stack is greater than the set threshold B, it is determined whether the absolute value of the difference between U1 and Umean1 is greater than the set threshold B. If so, the cathode of the battery is under-gassing. The set threshold B is 30mV.

8. The fuel cell stack offline quality monitoring method according to claim 7, Features: In the step 4), if the absolute value of the difference between the left and right sides of each battery in the stack is greater than the set threshold C, it is determined whether the absolute value of the difference between U2 and Umean2 is greater than the set threshold C. If so, the anode of the battery is under-gassing, and the set threshold C is 30mV.

9. A quality monitoring device for executing the quality monitoring method according to any one of claims 1 to 8, Features: The device is provided with a voltage collection connector connected to both sides of the bipolar plates of a single cell of the battery stack. The voltage collection connector is connected via a communication line and outputs a voltage signal to a voltage monitoring unit. The voltage monitoring unit is connected and outputs a voltage signal to a fuel cell test bench. The fuel cell test bench displays the collected voltage signal.

10. The fuel cell stack offline quality monitoring device according to claim 9, Features: Voltage collection connectors are inserted on both sides of each single-cell bipolar plate of the fuel cell stack, and each of the voltage collection connectors is connected to the voltage monitoring unit through CVP and CVM communication lines. The fuel cell test bench displays the voltage signals measured on the left and right sides of each battery in real time.

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