Alternating current impedance inspection test system of electric pile
By designing an AC impedance inspection and testing system for fuel cell stacks, the problem of measuring the AC impedance of high-power fuel cell stacks under operating conditions was solved. This system enables condition monitoring and fault diagnosis of fuel cell stack cells or cells, reducing safety risks and improving work efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- JIANGSU DONGHUA ANALYTICAL INSTR CO LTD
- Filing Date
- 2025-03-24
- Publication Date
- 2026-04-21
AI Technical Summary
Existing AC impedance testers cannot effectively measure the AC impedance of high-power fuel cell stacks under operating conditions, and are easily affected by external power sources or load interference, thus failing to meet the requirements for effective and reliable testing of high-power fuel cell stacks under operating conditions.
An AC impedance inspection and testing system for fuel cell stacks was designed, including a microprocessor, a control module, an excitation module, a signal acquisition module, and a signal analysis module. Through a specific combination and layout design, it can perform AC impedance measurement under the working state of high-power fuel cell stacks, reduce the influence of external interference, and realize the status monitoring and fault diagnosis of fuel cell stack cells or cells.
It enables accurate AC impedance measurement of high-power fuel cell stacks under operating conditions, reduces safety risks, improves stack efficiency, and provides fault diagnosis capabilities.
Smart Images
Figure CN224152564U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of electrochemical state monitoring technology, and more specifically, relates to an AC impedance inspection and testing system for fuel cell stacks. Background Technology
[0002] In the operation of new energy fuel cell stacks, the electrolytic cell stack is in a high-temperature, high-pressure, and sealed environment. Various battery stacks are also in a sealed state. Because it is impossible to install various sensors or detectors inside the cells or cells, it is difficult to obtain information about the internal operating status, efficiency, and the condition of components such as electrodes and separators. Currently, the operating status and fault status can only be determined by monitoring the voltage of each cell or cell. However, the working process of an electrochemical energy system stack is complex, involving the electrochemical reactions of various components, including electrodes, separators, electrolytes, and current collectors. The electrochemical processes include a series of electrochemical kinetic behaviors such as ion / gas adsorption / desorption, charge transfer, charge shift, and ion diffusion. Therefore, simply measuring the voltage of the electrolytic cell or battery cell, and obtaining the DC internal resistance from the open-circuit voltage, cannot reflect the complex internal electrochemical reactions and charge movement.
[0003] AC impedance spectroscopy, as a non-destructive, rapid, and effective method, is applied to the testing, analysis, and monitoring of fuel cell stacks. This technique can differentiate and deeply study the entire electrochemical kinetic process inside a cell or cell by applying a series of excitation current signals of different frequencies. Existing AC impedance spectroscopy instruments are mainly designed for laboratory-scale fuel cell stack testing and analysis. When the number of cells or cells is too large, leading to excessively high stack voltage, both excitation and measurement require tolerance to higher common-mode voltages. Furthermore, measurement accuracy issues remain for electrolyzer stacks with large film electrode areas ranging from tens to hundreds of microohms or for large-capacity battery stacks.
[0004] According to the principles and requirements of impedance testing, the applied excitation current ensures that the polarization voltage of the electrodes is in the linear region and higher than the power supply and system noise. For fuel cell stacks of hundreds of kilowatts and above, the ohmic impedance of the cells or cells is typically in the hundreds of microohms range, and the excitation current required for AC impedance testing can reach 30-100A. When testing electrolytic cells with a large number of cells or cells (e.g., more than 100) and high current (e.g., more than 1000A), the excitation power of the impedance testing equipment may reach tens or even hundreds of kilowatts. Considering the research and development, manufacturing difficulty, and cost of high-power impedance testers, as well as the significant system noise and power supply interference they generate during operation, current AC impedance testers are mainly used for testing and analyzing small laboratory-grade fuel cell stacks or medium-sized fuel cell stacks with voltages below 100 volts, or for static impedance measurement of high-power fuel cell stacks when not in operation. They cannot meet the impedance testing or monitoring needs of high-power fuel cell stacks in operation.
[0005] Therefore, there is an urgent need to develop effective and reliable impedance measurement technologies and corresponding testing systems for high-power fuel cell stacks with a large number of cells or cells and high current (more than 100 cells and more than 1000A). This will enable the AC impedance testing and monitoring of high-power fuel cell stacks under operating conditions. The technical challenge lies in ensuring that the AC impedance testing system can withstand high voltages under the operating conditions of the high-power fuel cell stack while avoiding or reducing interference from external power sources, loads, and system noise, thus enabling effective and reliable AC impedance testing of the fuel cell stack. Summary of the Invention
[0006] The purpose of this invention is to address the above-mentioned shortcomings by providing an AC impedance inspection and testing system for fuel cell stacks. This system can be applied to high-power fuel cell stacks. Through a specific combination and layout design of each module, it can measure the AC impedance of the fuel cell stack under operating conditions, characterizing the spatial and temporal differences of the cells or cells within the stack. This facilitates engineering technicians in studying and judging the state or faults of the fuel cell stack (including the cells or cells) and formulating relevant strategies and solutions. The system achieves the goal of monitoring the operating status of the fuel cell stack under test, effectively reducing safety risks and improving the working efficiency of the fuel cell stack.
[0007] To achieve the above objectives, this utility model is implemented through the following technical solution:
[0008] An AC impedance inspection test system for fuel cell stacks includes a microprocessor, a control module, an excitation module, a signal acquisition module, and a signal analysis module;
[0009] The microprocessor is communicatively connected to both the PC and the control module.
[0010] The excitation module is communicatively connected to the control module and electrically connected to the stack under test, and is used to apply an AC excitation current signal and a DC bias voltage signal to the stack under test.
[0011] The signal acquisition module is connected to the stack under test via a pre-isolation amplifier and is used to acquire the voltage signal of the stack under test and transmit it to the signal analysis module.
[0012] The signal analysis module is communicatively connected to the control module and the signal acquisition module, and transmits the calculated AC impedance data to the PC through the control module and the microprocessor.
[0013] Furthermore, the excitation module includes an electronic relay and a signal output module;
[0014] The electronic relay selects the output circuit of the signal output module according to the signal from the control module, which is used to switch the inspection and testing area of the fuel cell stack.
[0015] The signal output module is used to apply AC excitation current signal and DC bias voltage signal to a specified fuel cell stack area.
[0016] Furthermore, the signal output module includes an AC current output module and a DC voltage output modules, where a is the number of channels for measurable cells or cells in the selected stack inspection test area.
[0017] The AC current output module applies an AC excitation current signal to a designated fuel cell stack region;
[0018] The DC voltage output module applies a DC bias voltage signal to each cell or cell in the selected fuel cell stack inspection test area.
[0019] Furthermore, the test system also includes a sampling resistor for converting the current signal into a voltage signal. The sampling resistor is connected in series with the output circuit and placed at the negative terminal of the output circuit. The signal acquisition module acquires the voltage signal of each cell or cell in the selected fuel cell inspection test area from the sampling resistor. The voltage signal of each cell or cell in the selected fuel cell inspection test area is acquired through a pre-isolation amplifier.
[0020] Furthermore, the sampling resistor is a resistor with a fixed resistance value, ranging from 50 milliohms to 200 milliohms.
[0021] Furthermore, the pre-isolation amplifier is connected to each cell or cell in the battery stack under test, and acquires the voltage across the cells or cells via magnetic coupling, performs isolation amplification processing, and then transmits it to the signal acquisition module. The signal acquisition module includes a DC voltage acquisition submodule and an AC voltage acquisition submodule. The DC voltage acquisition submodule contains N+1 DC voltage acquisition channel units, where N is the total number of cells in the battery stack under test, N DC voltage acquisition channel units are used to acquire the DC voltage across the corresponding cells or cells, and 1 DC voltage acquisition channel unit is used to acquire the DC voltage across the sampling resistor. The AC voltage acquisition submodule contains N+1 AC voltage acquisition channel units, 1 AC voltage acquisition channel unit is used to acquire the AC voltage across the sampling resistor, N AC voltage acquisition channel units are used to acquire the AC voltage across the corresponding cells or cells, and a of the N AC voltage acquisition channel units are used to acquire the AC voltage across each cell or cell in the selected battery stack inspection test area, where a is the total number of channels for measurable cells or cells in the selected battery stack inspection test area.
[0022] Furthermore, the test system also includes a low-pass filter for tracking and filtering the voltage signal acquired by the pre-isolation amplifier and a gain amplifier for amplifying the filtered voltage signal; the low-pass filter is connected to the signal acquisition module through the gain amplifier.
[0023] Furthermore, the pre-isolation amplifier is used to receive and isolate a battery pack with a total voltage not exceeding 1000V.
[0024] Furthermore, the voltage range of the AC voltage acquisition submodule is 5 mV, 50 mV, 500 mV, or 5V.
[0025] Compared with the prior art, the beneficial effects of this utility model are as follows:
[0026] The AC impedance inspection and testing system described in this utility model is mainly used for battery stacks with a large number of cells or cells and a large current (e.g., ≥100 cells, ≥1000A). Through specific combination and layout design of each module, it can realize voltage monitoring and AC impedance inspection and testing of cells or cells under high-power battery stack operating conditions. It can complete voltage monitoring and impedance inspection of high-power battery stacks through a relatively low-power testing system, which can effectively reduce the cost of safety detection and monitoring of battery stacks, and can effectively analyze the working state inside the cells or cells of the battery stack, make fault diagnosis, and provide strong assistance for the safe operation and energy saving of electrolytic cell stacks or battery stacks. Attached Figure Description
[0027] Figure 1 A schematic diagram of the structure of an AC impedance inspection test system for a fuel cell stack is provided for an embodiment.
[0028] Figure 2 This is the signal transmission path for the open-circuit voltage detection in the AC impedance inspection test system described in the embodiment.
[0029] Figure 3 This refers to the signal transmission path for excitation testing in the AC impedance inspection test system described in the embodiment.
[0030] Figure 4 This is a schematic diagram illustrating the principle of the AC impedance inspection test method described in the embodiment. Detailed Implementation
[0031] The preferred embodiments of the present invention will now be described in more detail with reference to the accompanying drawings and specific examples.
[0032] The AC impedance method can obtain detailed information about the internal structure of an electrolytic cell or battery cell, including ohmic impedance, polarization impedance, and diffusion impedance.
[0033] In contrast to impedance testing systems, the battery under test (DUT) and the external power supply or load are connected in parallel. If an AC power amplifier is used for excitation, the excitation current will flow simultaneously through both the DUT and the external power supply or load. The power supply circuit, including resistors and capacitors, will then be introduced into the entire measurement circuit, interfering with the impedance measurement. While conventional impedance testing instruments may collect the true voltage value across the cell or battery cell, the current value collected for impedance calculation is the current output by the excitation module—the total current flowing through the battery stack and the power supply or load. This current is larger than the actual current flowing through the DUT, resulting in a calculated impedance that is smaller than the true value. Furthermore, a phase difference exists, leading to a deviation in the AC impedance measurement and preventing the acquisition of the true impedance value.
[0034] If an electronic load is used to pull an AC signal, the current flowing through the electrolytic cell stack will generate AC disturbance. However, the actual controllable or collectable current is the current pulled by the electronic load, and the true current value cannot be calculated, resulting in a deviation between the impedance value and the actual value.
[0035] To address these issues, a conventional method involves connecting a current sensor in series with the circuitry of the fuel cell stack under test (FCD) to collect the actual excitation current flowing through the stack. However, since the fuel cell stack is manufactured as a single, pressurized unit and cannot be disassembled, the current sensor can only be connected in series on either side of the end plate, i.e., the anode (negative) or cathode (positive). Therefore, the entire fuel cell stack must be excited to obtain the actual excitation current through the current sensor. When the number of cells or cells in the fuel cell stack is too large (e.g., exceeding 100) and the current is too high (e.g., exceeding 1000A), the excitation power during impedance testing may reach over 20kW. If the rated operating power of the fuel cell stack under test reaches the megawatt (MW) level, the excitation level of the power amplifier or electronic load used would need to reach over 100 kilowatts (100kW). Given current power supply technology, equipment size, construction difficulty, explosion-proof requirements, and operating costs, this is unsuitable and cannot be used in online monitoring systems for high-power fuel cell stacks.
[0036] The AC impedance inspection system of this utility model can achieve the purpose of measuring the impedance of high-power fuel cell stacks with low-power equipment. By optimizing the theory, technology and design of the inspection system, interference caused by the power supply circuit during impedance testing can be avoided or reduced, thereby achieving accurate measurement of the AC impedance of high-power fuel cell stacks. It can provide a reliable and effective technical means for monitoring the operating status of the cell and diagnosing faults during the operation of the fuel cell stack.
[0037] Example 1
[0038] This embodiment provides an AC impedance inspection and testing system for high-power electrolytic cell stacks, such as... Figure 1 As shown, it includes a microprocessor (ARM), a control module (FPGA), an excitation module, a signal acquisition module, and a signal analysis module (DSP).
[0039] The microprocessor is communicatively connected to both the PC and the control module.
[0040] The excitation module is communicatively connected to the control module and electrically connected to the stack under test, and is used to apply an AC excitation current signal and a DC bias voltage signal to the stack under test.
[0041] The signal acquisition module is connected to the stack under test via a preamplifier and is used to acquire the voltage signal of the stack under test and transmit it to the signal analysis module.
[0042] The signal analysis module is communicatively connected to the control module and the signal acquisition module, and transmits the calculated AC impedance data to the PC through the control module and the microprocessor.
[0043] Specifically, in this embodiment, the microprocessor ARM adopts the STM32F405RGT6 model microprocessor, which is used to receive instructions from the PC, process them, and send them to the control module FPGA; the control module FPGA adopts the EP4CGX30 model FPGA, which is used to receive signals from the microprocessor ARM, perform logic processing, and convert them into control signals to be sent to the excitation module and the signal analysis module.
[0044] In this embodiment, the excitation module includes an electronic relay and a signal output module. The electronic relay selects the output circuit of the signal output module according to the signal from the control module to switch the inspection test area of the fuel cell stack. Specifically, the control module controls the switch of the electronic relay to select different output paths to select the excitation circuit range of the fuel cell stack (i.e., the fuel cell stack area to perform the inspection test), and applies an AC current excitation signal to the selected fuel cell stack inspection test area through the AC current output module.
[0045] In this embodiment, the signal output module includes an AC current output module and *a* DC voltage output modules, where *a* represents the number of cells in the selected fuel cell inspection test area, i.e., the number of channels in the selected fuel cell inspection test area that can be measured in each inspection system. The AC current output module applies an AC current signal to the cells in the selected fuel cell inspection test area. When the AC current signal passes through the fuel cell in the selected fuel cell inspection test area, it affects the voltage of each cell in that area, making the voltage of each cell a vector sum of a DC open-circuit voltage and an AC feedback voltage. The *a* DC voltage output modules apply a negative voltage, completely opposite to the DC voltage of the corresponding cell, to each cell in the selected fuel cell inspection test area to cancel the DC open-circuit voltage of the cells in the selected fuel cell inspection test area; this is also called the DC bias voltage. In this embodiment, both the AC current output module and the DC voltage output module use TI's DAC8771 single-channel 16-bit current or voltage output digital-to-analog converter. The AC / DC current output module can apply an excitation current of 50A or more, up to a maximum of 100A.
[0046] In this embodiment, the signal acquisition module includes a DC voltage acquisition submodule, an AC voltage acquisition submodule, a sampling resistor, a gain amplifier, and a low-pass filter, such as... Figure 2 As shown; the sampling resistor is connected in series with the output circuit and placed at the negative terminal of the AC current output circuit. It can convert the current signal into a voltage signal. By acquiring the voltage and calculating it, the true value of the applied AC current can be obtained, which is used for subsequent AC impedance calculation. In this embodiment, the sampling resistor is a resistor with a fixed resistance value. The size of the fixed resistance value is selected according to the current size, and the resistance value range is 50-200 milliohms. The pre-isolation amplifier is connected to each cell in the stack under test and the signal acquisition module. In this embodiment, the pre-isolation amplifier uses the AD210 chip, which can be used to measure stacks with common mode voltage not exceeding 1000V and to isolate and amplify the acquired voltage signal. It has an Ex mb IIC T4 Gb explosion-proof rating and can be placed in the working site of stacks with explosion-proof requirements.
[0047] In this embodiment, the DC voltage acquisition submodule includes N+1 DC acquisition units; where N is the total number of cells in the battery stack under test, N acquisition channel units are used to acquire the DC voltage at both ends of the corresponding cell or cell, and 1 acquisition channel unit is used to acquire the DC voltage at both ends of the sampling resistor.
[0048] In this embodiment, the AC voltage acquisition submodule includes N+1 AC voltage acquisition channel units. One AC voltage acquisition channel unit is used to acquire the AC voltage across the sampling resistor, and the N AC voltage acquisition channel units are used to acquire the AC voltage across the corresponding cell. Among these, a+1 AC impedance sensing channel units are used to measure the cell impedance in the selected fuel cell inspection test area; where a is the number of cells in the selected fuel cell inspection test area. a AC current acquisition channel units, after activation, are used to acquire the AC voltage across each cell in the selected fuel cell inspection test area. The remaining AC impedance sensing channel unit is used to acquire the AC voltage across the sampling resistor. The voltage acquisition across the cells is performed using a pre-isolation amplifier via magnetic coupling. Both the DC voltage acquisition submodule and the AC voltage acquisition submodule in this embodiment use the AD7960 chip. The voltage range of the AC voltage acquisition submodule is 5 mV, 50 mV, 500 mV, or 5V.
[0049] like Figure 3 As shown, in this embodiment, both the AC voltage acquisition submodule and the DC voltage acquisition submodule are connected to a low-pass filter. The low-pass filter is connected to a pre-isolation amplifier to track and filter the response voltage signal of the small cell in the selected fuel cell inspection test area. In this embodiment, the low-pass filter is an 8th-order LTC1069-7 type low-pass filter. The low-pass filter is connected to the signal acquisition module through a gain amplifier. The function of the gain amplifier is to amplify the filtered voltage signal to a higher level so that the subsequent signal analysis module can perform effective impedance calculations.
[0050] In this embodiment, the signal acquisition module is connected to the signal analysis module (DSP) to convert the filtered and amplified voltage signal into a digital signal, which is then transmitted to the DSP for data analysis and calculation. The AC voltage acquisition submodule is connected to the DSP via a gain amplifier.
[0051] In this embodiment, the signal analysis module DSP uses TI's TMS320C6727B chip to analyze and calculate the received signal, and transmits the calculated voltage data or AC impedance data to the PC through the control module and microprocessor.
[0052] Example 2
[0053] This embodiment provides an AC impedance inspection and testing system for lithium-ion battery stacks, which performs AC impedance testing on the cells in the lithium-ion battery stack. Except for replacing the electrolytic cell stack with a lithium-ion battery stack and the small cell with a cell, the rest of the structure and function are the same as in Embodiment 1.
[0054] In some other embodiments, the AC impedance inspection and testing system can also be applied to energy systems such as flow battery stacks, sodium-ion battery stacks, and fuel cell stacks to perform AC impedance testing on the cells in the battery stack. Its structure and function are the same as in this embodiment, and will not be described again in this invention.
[0055] Example 3
[0056] This embodiment provides a method for performing AC impedance inspection on an electrolytic cell stack using the AC impedance inspection system described in Embodiment 1, specifically including the following steps:
[0057] Step 1: After the electrolytic cell stack to be measured is connected to a three-way power supply or load, the voltage of each cell in the electrolytic cell stack is processed by a pre-isolation amplifier and then sent to the signal acquisition module. After analog-to-digital conversion and other processing, it is sent to the signal analysis module DSP.
[0058] Step 2: After receiving and processing the instructions from the PC, the microprocessor ARM sends them to the control module FPGA. The control module FPGA, upon receiving the instruction signal from the microprocessor ARM, performs logic processing and converts it into a control signal, which is then communicated with the signal analysis module DSP. The signal analysis module performs calculations and processing on the digital signal input from the signal acquisition module based on the control signal from the control module, obtaining the open-circuit voltage of the chamber. The processed open-circuit voltage signal is then transmitted to the PC via the control module and the microprocessor, and displayed at a preset refresh rate. The signal transmission path in the above steps is as follows: Figure 2 As shown;
[0059] Step 3: The microprocessor ARM receives the preset cell voltage abnormality alarm and impedance test or impedance inspection command from the PC and sends it to the control module FPGA; the control module FPGA receives the signal from the microprocessor ARM, performs logic processing, and then applies an AC current excitation signal to the stack area where the voltage abnormality cell is located or the preset stack area to be inspected through the AC current output module of the excitation module.
[0060] Step 4: The control module FPGA converts the instruction signal into a circuit logic control signal and transmits it to the DC voltage output module of the excitation module while executing step 3, based on the open circuit voltage of the small cell collected in step 2, and outputs the corresponding DC voltage to the front end of the acquisition module.
[0061] Step 5: The signal acquisition module processes and converts the voltage signals input in Step 1 and Step 4, and simultaneously transmits the AC voltage component values (filtered AC voltage signals) acquired from both ends of the sampling resistor and the small cell of the fuel cell to the signal analysis module DSP (i.e., the digital signal analysis and processing module in the figure) through the AC voltage acquisition module.
[0062] Step 6: The signal analysis module DSP calculates the ratio of the AC voltage across the sampling resistor to the resistance in real time to obtain the AC current, and calculates the ratio of the AC voltage across the sampled chamber to the AC current to obtain the AC impedance of the test chamber; the signal transmission path in the above steps is as follows: Figure 3 As shown;
[0063] Step 7: If the system is set to patrol inspection mode, after the impedance measurement of the cell in the selected fuel cell patrol inspection test area is completed, the microprocessor ARM will send the switching command to the control module FPGA according to the patrol inspection program settings. The FPGA will process the command and control the electronic relay through the logic circuit to select and switch the output circuit of the AC current output module, thereby stimulating the electrolytic cell of the next fuel cell patrol inspection area. Then the entire AC impedance patrol inspection system repeats the operation of steps 3 to 6 until all the electrolytic cells in all the set fuel cell patrol inspection areas have completed the impedance measurement.
[0064] In the above steps, the calculation process of the signal analysis module DSP includes:
[0065] If, in step 3, the AC current output module applies an AC current excitation signal of a set frequency to the selected fuel cell inspection test area (the fuel cell area where the voltage anomaly cell is located or the fuel cell area of the preset quantity to be inspected), the test impedance value of the cell within the selected fuel cell inspection test area can be calculated. The calculation formula is as follows:
[0066] ;
[0067] in, To select the first in the stack inspection test Impedance test values of each small chamber. To select the first test area for fuel cell stack inspection AC voltage measurement values for each small chamber. This refers to the total excitation current output by the AC current output module.
[0068] If, in step 3, the AC current output module applies an AC current excitation signal with a scanning frequency to the selected fuel cell inspection test area, then the AC impedance modulus of the cell is utilized. Phase difference between AC voltage and AC current at different frequencies The real part Zre and the imaginary part Zim of the AC impedance of the cell are calculated in real time. The calculation formula is as follows:
[0069] ;
[0070] ;
[0071] This allows us to obtain the test impedance value of the selected cell or cell in the fuel cell inspection test area, expressed as:
[0072] ;
[0073] in, To select the first test area for fuel cell stack inspection The real part of the impedance of a small cell or battery cell To select the first test area for fuel cell stack inspection The imaginary part of the impedance of each small cell.
[0074] like Figure 4 As shown, when the number of cells in the fuel cell stack is too large and the current is too high, it is impossible to excite and test the entire fuel cell stack in series at the same time. Only the cells in the selected fuel cell stack inspection and testing area are subjected to impedance testing and analysis. Therefore, the unselected parts of the fuel cell stack are not within the scope of testing and research, but they will form a parallel circuit with the area to be inspected and tested and the power supply or load will be connected in series into the parallel circuit.
[0075] Therefore, during impedance testing, the total excitation current output by the AC current output module is... Because the inspection and testing area and the non-test area are connected in parallel, the current will be divided between the areas flowing through the inspection and testing area. and non-test areas The AC voltage measurement of the small room in the test area to be inspected is as follows: Then its impedance calculation formula is: However, the current collected by conventional instruments or testing systems is actually the total excitation current. Therefore, the impedance calculated using the instrument is: The deviation between the actual impedance value and the measured impedance value, BR, can be calculated using the following formula:
[0076] ;
[0077] And because Because the potentials of parallel circuits are the same, Finally, we can obtain:
[0078] ;
[0079] Where BR is the deviation rate between the actual impedance value and the test impedance value; N is the total number of cells in the entire stack under test.
[0080] Alternatively, the deviation can be expressed as the ratio of the tested impedance value to the true impedance value, as shown in the following formula.
[0081] ;
[0082] in, It is the ratio of the test impedance value to the true impedance value. The closer the value is to 1 (i.e., the smaller the a / N), the closer the test impedance value is to the true impedance value.
[0083] By replacing the small chamber with a battery cell, the inspection and testing method described in this embodiment can also be used for impedance measurement of battery stacks. The steps and calculation methods are the same as in this embodiment, and will not be repeated here.
[0084] As can be seen from the above formula, the more cells or cells in the tested fuel cell stack, and the fewer cells or cells in the inspection area, the closer the instrument's measurement value is to the true value. When the selected number of cells or cells to be inspected is 2% of the total number of cells (e.g., 8 cells or cells in the inspection area and 400 cells or cells in the total fuel cell stack), the instrument's measurement value is 98% of the true value. If the number of cells or cells inspected is less than 4, the impedance deviation can be controlled to be less than 1%. This means the impedance value measured by the instrument can be considered the true value, or the measured impedance value can be considered to have high accuracy. This solves the problem that conventional instruments cannot measure high-power fuel cell stacks with a large number of cells or cells and high current, or the deviation is large.
[0085] If the effects of the power supply or load cannot be ignored, then the impedance characteristics of the power supply or load need to be considered. Since the power supply is part of an AC / CD circuit, it can be considered as a large capacitor, for example... Similarly, the following relationship also exists:
[0086] ,
[0087] Similarly, it can be calculated based on the fact that the voltages in parallel circuits are equal.
[0088] ;
[0089] in, The angular frequency of the excitation current for impedance testing; This refers to the capacitance value of the power supply or load.
[0090] As can be seen from the above analysis, the lower the frequency, the smaller the impedance between the power supply or load capacitor and the cell or cell, and the smaller the impact of the power supply or load and the unselected measurement area. Therefore, the AC impedance inspection test system and method involved in this invention can fill the technical gap in AC impedance testing of high-power battery stacks through system design, effectively solving problems such as high power, high cost, difficulty in explosion protection, and inaccurate data in measurement, and thus can be applied to the field of AC impedance testing of high-power battery stacks with a large number of cells or cells and a large current (more than 100 cells or cells, and a current exceeding 1000A).
[0091] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and technical principles of the described embodiments, and these modifications and variations should also be considered within the scope of protection of the present invention.
Claims
1. An AC impedance patrol test system for a stack, characterized by, It includes a microprocessor, a control module, an excitation module, a signal acquisition module, and a signal analysis module; The microprocessor is communicatively connected to both the PC and the control module. The excitation module is communicatively connected to the control module and electrically connected to the stack under test, and is used to apply an AC excitation current signal and a DC bias voltage signal to the stack under test. The signal acquisition module is connected to the stack under test via a pre-isolation amplifier and is used to acquire the voltage signal of the stack under test and transmit it to the signal analysis module. The signal analysis module is communicatively connected to the control module and the signal acquisition module, and transmits the calculated AC impedance data to the PC through the control module and the microprocessor.
2. The AC impedance patrol test system of the electric pile according to claim 1, characterized in that, The excitation module includes an electronic relay and a signal output module; The electronic relay selects the output circuit of the signal output module according to the signal from the control module, which is used to switch the inspection and testing area of the fuel cell stack. The signal output module is used to apply AC excitation current signal and DC bias voltage signal to a specified fuel cell stack area.
3. The AC impedance patrol test system of the electric pile according to claim 2, characterized in that, The signal output module includes an AC current output module and a DC voltage output modules, where a is the number of channels for measurable cells or cells in the selected fuel cell inspection test area. The AC current output module applies an AC excitation current signal to a designated fuel cell stack region; The DC voltage output module applies a DC bias voltage signal to each cell or cell in the selected fuel cell stack inspection test area.
4. The AC impedance patrol test system of the electric pile according to claim 1, characterized in that, It also includes a sampling resistor for converting the current signal into a voltage signal, the sampling resistor being connected in series with the output circuit and placed at the negative terminal of the output circuit; The signal acquisition module acquires the sampling resistor and the voltage signal of each cell or cell in the selected fuel cell inspection test area; wherein, the voltage signal of each cell or cell in the selected fuel cell inspection test area is acquired through a pre-isolation amplifier.
5. The AC impedance patrol test system of the electric pile according to claim 4, characterized in that, The sampling resistor is a resistor with a fixed resistance value, ranging from 50 milliohms to 200 milliohms.
6. The AC impedance patrol test system of the electric pile according to claim 4, characterized in that, The pre-isolation amplifier is connected to each cell or cell in the stack under test. It acquires the voltage across the cells or cells via magnetic coupling, performs isolation amplification, and then transmits the signal to the signal acquisition module. The signal acquisition module includes a DC voltage acquisition submodule and an AC voltage acquisition submodule; The DC voltage acquisition submodule includes N+1 DC voltage acquisition channel units; where N is the total number of cells in the battery stack under test, N DC voltage acquisition channel units are used to acquire the DC voltage at both ends of the corresponding cell or cell, and 1 DC voltage acquisition channel unit is used to acquire the DC voltage at both ends of the sampling resistor. The AC voltage acquisition submodule includes N+1 AC voltage acquisition channel units. One AC voltage acquisition channel unit is used to acquire the AC voltage across the sampling resistor. The N AC voltage acquisition channel units are used to acquire the AC voltage across the corresponding cell or cell. Among the N AC voltage acquisition channel units, a AC voltage acquisition channel units are used to acquire the AC voltage across each cell or cell in the selected fuel cell inspection test area. Here, a is the number of channels that can be used to measure cells or cells in the selected fuel cell inspection test area.
7. The AC impedance patrol test system of the stack according to claim 6, wherein, It also includes a low-pass filter for tracking and filtering the voltage signal acquired by the pre-isolation amplifier and a gain amplifier for amplifying the filtered voltage signal; the low-pass filter is connected to the signal acquisition module through the gain amplifier.
8. The AC impedance patrol test system of the electric pile according to claim 4, characterized in that, The pre-isolation amplifier is used to receive and isolate amplify fuel cells with a total voltage not exceeding 1000V.
9. The AC impedance patrol test system of the stack according to claim 6, characterized by, The voltage range of the AC voltage acquisition submodule is 5 mV, 50 mV, 500 mV, or 5V.