Alternating current impedance inspection test system and test method for galvanic pile

Abstract

The invention discloses an alternating current impedance inspection test system and test method of a galvanic pile in the technical field of electrochemical state monitoring. The system comprises a microprocessor, a control module, an excitation module, a signal acquisition module and a signal analysis module, the microprocessor is in communication connection with the PC terminal and the control module. The excitation module is in communication connection with the control module, is electrically connected with a to-be-tested electric pile, and applies an alternating current excitation current signal and a direct current bias voltage signal to the to-be-tested electric pile; the signal acquisition module is connected with a to-be-tested galvanic pile through a front isolation amplifier, acquires a voltage signal of the to-be-tested galvanic pile and transmits the voltage signal to the signal analysis module; the signal analysis module is in communication connection with the control module and the signal acquisition module, and transmits calculated AC impedance data to a PC terminal through the control module and the microprocessor. According to the invention, alternating-current impedance inspection testing can be carried out on a small chamber or a cell under the working state of the high-power galvanic pile, so that the state or fault of the galvanic pile can be conveniently researched and judged, and related strategies and solutions can be formulated.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical state monitoring, and more specifically, relates to an alternating current impedance patrol detection test system and a test method for an electrolyzer stack. Background Art

[0002] When a new energy electrolyzer stack is in operation, the electrolyzer stack of the electrolytic cell is in a sealed environment of high temperature and high pressure, and various battery stacks are also in a sealed state. Since various sensors or detectors cannot be added inside the small chambers or battery cells, it is very difficult to obtain the operating state, working efficiency, and the integrity of components such as electrodes and diaphragms inside the small chambers or battery cells. Currently, it is only possible to judge its working state and whether there is a fault by monitoring the voltage of each small chamber or battery cell. However, the working process of the electrolyzer stack of the electrochemical energy system is complex and involves the electrochemical reaction processes of various components. The components include electrodes, diaphragms, electrolytes, current collectors, etc. The electrochemical processes include a series of electrochemical kinetic behaviors such as ion / gas adsorption and desorption, charge transfer, charge migration, and ion diffusion. Therefore, simply measuring the voltage of the small chambers of the electrolytic cell or the battery cells and the DC internal resistance obtained through the open circuit voltage cannot reflect the complex electrochemical reactions and charge movement inside.

[0003] The alternating current impedance technology is applied to the test analysis and monitoring judgment of the electrolyzer stack as a non-destructive, fast and effective method. This technology can distinguish and deeply study the entire electrochemical kinetic process inside the small chambers or battery cells by applying a series of excitation current signals with different frequencies. The existing alternating current impedance testers are mainly aimed at the test and analysis of laboratory-level electrolyzer stacks. When the number of small chambers or battery cells is too large, resulting in too high a voltage of the electrolyzer stack, both excitation and measurement need to withstand a higher common mode voltage. In addition, there are also measurement accuracy problems for electrolyzer stacks with large membrane electrode areas of dozens to hundreds of micro-ohms or large-capacity battery stacks.

[0004] According to the impedance test principle and requirements, the applied excitation current makes the polarization voltage of the electrode in the linear region and higher than the power supply and system noise. For electrolyzer stacks with a power of one hundred kilowatts or more, the ohmic impedance of their small chambers or battery cells is usually in the order of hundreds of micro-ohms, and the excitation current required for alternating current impedance testing will reach 30 - 100 A. When it is necessary to test an electrolytic cell with a large number of small chambers or battery cells (for example, the number exceeds 100) and a large current (for example, the current exceeds 1000 A), the excitation power of the impedance test equipment may also reach dozens or even one hundred kilowatts. Considering the R & D, manufacturing difficulty and usage cost of the high-power impedance tester itself, and the large system noise and power supply interference it will bring during operation, the current alternating current impedance testers are mainly aimed at the test and analysis of laboratory-level small electrolyzer stacks or medium-sized electrolyzer stacks with a voltage within one hundred volts, or the static impedance measurement of high-power electrolyzer stacks when they are not working, and cannot meet the impedance test or monitoring requirements of high-power electrolyzer stacks in the working state.

[0005] Therefore, there is an urgent need to develop an effective and reliable impedance measurement technology and corresponding test system for high-power stacks with a large number of cells or modules and high current (more than 100 cells or modules and more than 1000 A current) to achieve the AC impedance test and monitoring of high-power stacks under operating conditions. The difficulty of this technology lies in that the AC impedance test system can withstand high voltages under the operating state of high-power stacks and can avoid or reduce the interference effects brought by external power supplies, loads, and system noises to effectively and reliably test the AC impedance of the stacks. Summary of the Invention

[0006] The object of the present invention is to provide an AC impedance patrol test system and test method for stacks, which can be applied to high-power stacks, measure the AC impedance of the stacks under the operating state, characterize the spatial and temporal differences of cells or modules in the stacks, facilitate engineers and technicians to study and judge the state or faults of the stacks (cells or modules therein) and formulate relevant strategies and solutions, achieve the purpose of monitoring the operating state of the stacks to be tested, effectively reduce safety risks, and improve the operating efficiency of the stacks.

[0007] To achieve the above object, the present invention is realized through the following technical solutions: In the first aspect, the present invention provides an AC impedance patrol test system for stacks, including a microprocessor, a control module, an excitation module, a signal acquisition module, and a signal analysis module; The microprocessor is communicatively connected to the PC terminal and the control module respectively; The excitation module is communicatively connected to the control module and electrically connected to the stack to be tested, and is used to apply an AC excitation current signal and a DC bias voltage signal to the stack to be tested; The signal acquisition module is connected to the stack to be tested through a pre-isolation amplifier, and is used to collect the voltage signal of the stack to be tested 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 terminal through the control module and the microprocessor.

[0008] Further, 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 of the control module and is used to switch the patrol test area of the stack; the signal output module includes an AC current output module and a DC voltage output modules, where a is the total number of channels of measurable cells or modules in the selected patrol test area of the stack; the AC current output module applies an AC excitation current signal to both ends of the stack in the selected patrol test area of the stack; the DC voltage output module applies a DC bias voltage signal to each cell or module in the selected patrol test area of the stack.

[0009] Further, the test system further includes a sampling resistor for converting a 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 signals of the sampling resistor and each cell or battery core in the selected fuel cell stack inspection and test area; wherein, the voltage signals of each cell or battery core in the selected fuel cell stack inspection and test area are acquired through a pre-isolation amplifier.

[0010] Further, the pre-isolation amplifier is connected to each cell or battery core in the fuel cell stack to be tested, acquires the voltage across the cell or battery core through magnetic coupling, performs isolation amplification processing, and then transmits it to the signal acquisition module; the signal acquisition module includes a DC voltage acquisition sub-module and an AC voltage acquisition sub-module; the DC voltage acquisition sub-module includes N + 1 DC voltage acquisition channel units; where N is the total number of cells in the fuel cell stack to be tested, and N DC voltage acquisition channel units are respectively used to acquire the DC voltages across the corresponding cells or battery cores, and 1 DC voltage acquisition channel unit is used to acquire the DC voltage across the sampling resistor; the AC voltage acquisition sub-module includes N + 1 AC voltage acquisition channel units, 1 AC voltage acquisition channel unit is used to acquire the AC voltage across the sampling resistor, and N AC voltage acquisition channel units are respectively used to acquire the AC voltages across the corresponding cells or battery cores, and among the N AC voltage acquisition channel units, a AC voltage acquisition channel units are respectively used to acquire the AC voltages across each cell or battery core in the selected fuel cell stack inspection and test area; where a is the total number of channels of the measurable cells or battery cores in the selected fuel cell stack inspection and test area.

[0011] Further, the test system further includes a low-pass filter for performing tracking filtering on the voltage signals acquired by the pre-isolation amplifier and a gain amplifier for amplifying the filtered voltage signals; the low-pass filter is connected to the signal acquisition module through the gain amplifier.

[0012] In a second aspect, the present invention also provides a method for AC impedance inspection and testing of a fuel cell stack. Based on the test system described in the first aspect, it includes: Step a: The signal acquisition module acquires the initial voltage signals of all cells or battery cores of the fuel cell stack to be measured through a pre-amplifier, processes them, and then transmits them to the signal analysis module. The signal analysis module processes the initial voltage signals of the signal acquisition module according to the control signals of the control module to obtain the open-circuit voltages of all cells or battery cores of the fuel cell stack to be measured, and transmits the open-circuit voltages to the PC through the control module and the microprocessor. Step b: The control module receives the command signal from the PC through the microprocessor, combines the command signal and the open-circuit voltage, and sends an excitation control signal to the excitation module, and applies an AC excitation current signal and a DC bias voltage signal to the selected fuel cell stack inspection and test area through the excitation module. Step c: The signal acquisition module collects the voltage signals of the cells or battery cores in the selected cell stack inspection test area after excitation through a preamplifier, and after processing, transmits them to the signal analysis module; Step d: The signal analysis module calculates the AC impedance of the cells or battery cores in the selected cell stack inspection test area based on the signals transmitted by the signal acquisition module, and transmits it to the PC through the control module and the microprocessor; Repeat the operations of Step b to Step d until the impedance test of the cells or battery cores in the last inspection test area is completed.

[0013] Further, applying the excitation current signal and voltage signal to the selected cell stack inspection test area by the excitation module includes: Applying an alternating current signal to the selected cell stack inspection test area through the alternating current output module; Outputting a corresponding DC voltage to the front end of the acquisition module in the selected cell stack inspection test area through the DC voltage output module.

[0014] Further, the command signal of the PC is an alarm for abnormal voltage of the cell or battery core and an impedance test command or an impedance inspection command; the selected cell stack inspection test area is the cell stack inspection area where the excitation module is sequentially activated according to a preset rule in the entire cell stack to be measured, or the cell stack inspection area where the cell or battery core with abnormal voltage is located.

[0015] Further, the signal analysis module calculates the AC impedance of the cell or battery core to be measured based on the signals transmitted by the signal acquisition module, including: If in Step b, the alternating current output module in the excitation module applies an alternating current excitation signal with a set frequency to the selected cell stack inspection test area, and obtains the test impedance value of the cells or battery cores in the selected cell stack inspection test area, and its calculation formula is: ; Wherein, is the test impedance value of the th cell or battery core in the selected cell stack inspection test area, is the measured value of the alternating current voltage of the th cell or battery core in the selected cell stack inspection test area, is the total excitation current output by the alternating current output module.

[0016] Further, the signal analysis module calculates the AC impedance of the cell or battery core to be measured based on the signals transmitted by the signal acquisition module, and further includes: If in Step b, the alternating current output module in the excitation module applies an alternating current excitation signal with a scanning frequency to the selected cell stack inspection test area, then use the modulus of the AC impedance of the cell or battery core The phase difference between the AC voltage and the AC current at different frequencies , calculate the real part Zre and the imaginary part Zim of the AC impedance of the small chamber or the battery cell in real time. The calculation formula is as follows: ; ; Furthermore, obtain the test impedance value of the small chamber or the battery cell in the selected stack inspection and test area. Its expression is: ;

[0017] Among them, is the real part of the impedance of the th small chamber or battery cell in the selected stack inspection and test area, is the imaginary part of the impedance of the th small chamber in the selected stack inspection and test area.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The AC impedance inspection and test system described in the present invention is mainly used for stacks with a large number of small chambers or battery cells and a large current (such as the number of small chambers ≥ 100, current ≥ 1000 A). It can realize voltage monitoring and AC impedance inspection and test of the small chambers or battery cells of the stack under the working state of high-power stacks; it completes voltage monitoring and impedance inspection of high-power stacks through a relatively low-power test system, which can effectively reduce the safety detection and monitoring costs of the stack, and can effectively analyze the internal working state of the small chambers or battery cells of the stack, make fault diagnosis, and provide strong help for the safe operation, energy conservation and efficiency improvement of the electrolytic cell stack or the battery stack; The AC impedance inspection and test method described in the present invention can real-time monitor the open-circuit voltage of each small chamber or battery cell when multiple small chambers or battery cells in the stack are working simultaneously, and can also perform impedance inspection and test on all small chambers or battery cells through the inspection mode or only perform precise AC impedance test on the stack area where the small chambers or battery cells with abnormal open-circuit voltage are located, so as to achieve the purpose of monitoring the internal electrochemical state of all small chambers or battery cells in the stack. The test system and method can effectively know the real operating condition of the stack, diagnose abnormalities and faults, so as to ensure the safety, reliability and efficiency of the stack during operation; The method described in the present invention can avoid or reduce the interference brought by the power supply or load circuit during impedance test through the special design of the inspection system, thereby improving the impedance measurement accuracy of the stack, and the high-precision impedance value obtained through measurement can be used to efficiently analyze the operating state and fault conditions of the stack. Brief Description of the Drawings

[0019] Figure 1 is a schematic structural diagram of an AC impedance inspection and test system for a stack provided by an embodiment of the present invention; Figure 2 The detection signal transmission path of the open-circuit voltage in the AC impedance patrol detection test system described in the embodiment; Figure 3 The signal transmission path of the excitation test in the AC impedance patrol detection test system described in the embodiment; Figure 4 It is a schematic diagram of the principle of the AC impedance patrol detection method described in the embodiment. Specific embodiments

[0020] The preferred embodiments of the present invention will be described in more detail below in conjunction with the accompanying drawings and specific embodiments.

[0021] Detailed information such as ohmic impedance, polarization impedance, and diffusion impedance inside the electrolytic cell compartment or battery cell can be obtained through the method of AC impedance.

[0022] Relative to the impedance test system, the stack under test is in a parallel mode with an external power source or load. If an AC power amplifier is used for excitation, the excitation current will flow through both the stack under test and the external power source or load simultaneously. If the power supply circuit includes resistors and capacitors, it will be introduced into the entire measurement circuit, causing interference to the impedance measurement. At this time, although the voltage across the compartment or cell collected by a conventional impedance test instrument is the true voltage value, the current value collected for impedance calculation is the current output by the excitation module, that is, the total current passing through the stack and the power source or load part, which is larger than the actual current flowing through the stack under test. Therefore, the calculated impedance is smaller than the true value, and there is also a phase difference, resulting in a test deviation of the AC impedance and an inability to obtain the true impedance value.

[0023] If an electronic load is used to pull an AC signal, the current flowing through the electrolytic cell stack will form an AC perturbation, but the actually controllable or collectable current is the current pulled by the electronic load, and the true current value cannot be calculated either, resulting in a deviation between the impedance value and the actual value.

[0024] To solve the above problems, the conventional method is to connect a current sensor in series in the circuit of the stack under test to collect the true excitation current passing through the stack. However, the stack is manufactured under overall pressure and cannot be disassembled. The current sensor can only be connected in series on both sides of the end plate, that is, the anode (negative electrode) or the cathode (positive electrode). Therefore, the stack under test must be excited as a whole to obtain the true excitation current through the current sensor. When the number of compartments or cells in the stack is too large (for example, more than 100), and the current is too large (for example, more than 1000A), the excitation power during impedance testing may reach more than 20kW. If the rated operating power of the stack under test reaches the megawatt (MW) level, the excitation level of the power amplifier or electronic load used needs to reach more than 100kW. Whether it is the current power supply technology, the equipment volume, the construction difficulty, the explosion-proof requirements, or the use cost, it is not suitable and cannot be used for the on-line monitoring system of high-power energy stack systems.

[0025] The AC impedance inspection system involved in the present invention can achieve the purpose of measuring the impedance of a high-power stack with a low-power device, and can avoid or reduce the interference brought by the power supply circuit during impedance testing through the optimization of aspects such as the theory, technology, and design of the inspection system, so as to achieve the accurate measurement of the AC impedance of the high-power stack, and can provide a reliable and effective technical means for the operation status monitoring and fault diagnosis of the small chambers during the operation of the stack.

[0026] Embodiment 1 This embodiment provides an AC impedance inspection and testing system applied to a high-power electrolytic cell stack, as Figure 1 shown, including a microprocessor (ARM), a control module (FPGA), an excitation module, a signal acquisition module, and a signal analysis module (DSP); The microprocessor is communicatively connected to the PC terminal and the control module respectively; The excitation module is communicatively connected to the control module and electrically connected to the stack to be tested, and is used to apply an AC excitation current signal and a DC bias voltage signal to the stack to be tested; The signal acquisition module is connected to the stack to be tested through a preamplifier, and is used to collect the voltage signal of the stack to be tested 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 terminal through the control module and the microprocessor.

[0027] Specifically, in this embodiment, the microprocessor ARM uses a microprocessor of the STM32F405RGT6 model, which is used to receive the instructions from the PC terminal, process them, and then send them to the control module FPGA; the control module FPGA uses an FPGA of the EP4CGX30 model, which is used to receive the signals from the microprocessor ARM, perform logical processing, and then convert them into control signals and transmit them to the excitation module and the signal analysis module.

[0028] In this embodiment, the excitation module includes an electronic relay and a signal output module; the electronic relay selects the output loop of the signal output module according to the signal of the control module, and is used to switch the inspection and testing area of the stack; specifically, the control module controls the switch of the electronic relay to select different output paths to determine the excitation loop range of the stack (i.e., the stack area where the inspection and testing are performed), and applies an AC current excitation signal to the selected stack inspection and testing area through the AC current output module.

[0029] In this embodiment, the signal output module includes an alternating current output module and a direct current voltage output module, where a is the number of cells in the selected fuel cell stack inspection test area, that is, the number of channels of the measurable cells in the fuel cell stack inspection test area each time in the inspection system; the alternating current output module applies an alternating current signal to the cells in the selected fuel cell stack inspection test area; when the alternating current signal passes through the fuel cell stack in the selected fuel cell stack inspection test area, it will affect the voltage of each cell in this area, making the voltage of each cell the vector sum of a direct current open-circuit voltage and an alternating current feedback voltage; the a direct current voltage output modules apply negative voltages that are exactly opposite to the direct current voltages of the corresponding cells to each cell in the selected fuel cell stack inspection test area, which is used to cancel the direct current open-circuit voltage of the cells in the selected fuel cell stack inspection test area, and is also called the direct current bias voltage. In this embodiment, both the alternating current output module and the direct current voltage output module use the TI DAC8771 single-channel 16-bit current or voltage output digital-to-analog converter; the alternating and direct current output module can apply an excitation current of 50 A or more, up to 100 A.

[0030] In this embodiment, the signal acquisition module includes a direct current voltage acquisition sub-module, an alternating current voltage acquisition sub-module, a sampling resistor, a gain amplifier, and a low-pass filter, as Figure 2 shown; the sampling resistor is connected in series with the output circuit and is placed at the negative terminal of the alternating current output circuit. It can convert the current signal into a voltage signal. By collecting its voltage and calculating, the true value of the applied alternating current can be obtained for subsequent alternating current impedance calculation. In this embodiment, the sampling resistor uses a resistor with a fixed resistance value, and the size of the resistor with a fixed resistance value is selected according to the current magnitude, and the resistance value range is 50 - 200 milliohms; the pre-isolation amplifier is respectively connected to each cell in the fuel cell stack to be measured and the signal acquisition module. In this embodiment, the pre-isolation amplifier selects the AD210 chip, which can be used to measure fuel cell stacks with a common-mode voltage not exceeding 1000 V and perform isolation amplification processing on the collected voltage signals. It has an Ex mb IIC T4 Gb explosion-proof rating and can be placed at the working site of fuel cell stacks with explosion-proof requirements.

[0031] In this embodiment, the direct current voltage acquisition sub-module includes N + 1 direct current acquisition units; where N is the total number of cells in the fuel cell stack to be measured, and N acquisition channel units are respectively used to acquire the direct current voltages at both ends of the corresponding cells or battery cores, and 1 acquisition channel unit is used to acquire the direct current voltage across the sampling resistor; In this embodiment, the AC voltage acquisition sub-module 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 N AC voltage acquisition channel units are respectively used to acquire the AC voltages across the corresponding compartments at both ends; among them, there are a + 1 AC impedance patrol measurement channel units for measuring the impedance of the compartments in the selected stack patrol test area; where a is the number of compartments in the selected stack patrol test area, and a AC current acquisition channel units are used to acquire the AC voltages across each compartment in the selected stack patrol test area after activation; the remaining one AC impedance patrol measurement channel unit is used to acquire the AC voltage across the sampling resistor. The voltage acquisition across the above-mentioned compartments at both ends is all acquired by a front-end isolation amplifier through magnetic coupling. The DC voltage acquisition sub-module and the AC voltage acquisition sub-module in this embodiment both select the AD7960 chip, and the voltage range of the AC voltage acquisition sub-module is 5 mV or 50 mV or 500 mV or 5V.

[0032] As Figure 3 shown, in this embodiment, both the AC voltage acquisition sub-module and the DC voltage acquisition sub-module are connected to a low-pass filter. The low-pass filter is connected to a front-end isolation amplifier to perform tracking filtering on the response voltage signal of the compartments in the selected stack patrol test area. The low-pass filter in this embodiment uses an LTC1069-7 type 8th-order low-pass filter; the low-pass filter is connected to a signal acquisition module through a gain amplifier. The function of the gain amplifier is to amplify the filtered voltage signal to a higher level for effective impedance calculation by the subsequent signal analysis module.

[0033] The signal acquisition module in this embodiment is connected to the signal analysis module DSP, and is used to convert the filtered and amplified voltage signal into a digital signal and transmit it to the signal analysis module DSP for data analysis and calculation. The AC voltage acquisition sub-module is connected to the signal analysis module DSP through a gain amplifier.

[0034] In this embodiment, the signal analysis module DSP uses the TI's TMS320C6727B chip, which is used to perform analysis and calculation according to the received signal, and transmit the calculated voltage data or AC impedance data to the PC through the control module and the microprocessor.

[0035] In some other embodiments, the AC impedance patrol test system can also be applied to energy systems such as lithium-ion battery stacks, flow battery stacks, sodium-ion battery stacks, and fuel cell stacks to perform AC impedance tests on the battery cells (equivalent to compartments in the structure of the test system). Its structure and function are the same as those in this embodiment, and the present invention will not be elaborated here.

[0036] Embodiment 2 This embodiment provides a method for AC impedance patrol detection test of an electrolyzer stack. Based on the test system described in Embodiment 1, the test method specifically includes the following steps: Step 1: After the electrolyzer stack to be measured works with a three - party power supply or load, the voltages of each small chamber in the electrolyzer stack are processed by a pre - isolation amplifier and then sent to a signal acquisition module, and after processing such as analog - to - digital conversion, they are sent to a signal analysis module DSP; Step 2: The microprocessor ARM receives instructions from the PC side, processes them and sends them to the control module FPGA. After receiving the instruction signal from the microprocessor ARM, the control module FPGA performs logical processing, converts it into a control signal and communicates with the signal analysis module DSP. The signal analysis module performs operations and processing on the digital signals input by the signal acquisition module according to the control signal of the control module, obtains the open - circuit voltage of the small chamber, and transmits the obtained open - circuit voltage signal to the PC side through the control module and the microprocessor, and outputs and displays the open - circuit voltage of the small chamber at a preset refresh frequency; The signal transmission path in the above steps is as Figure 2 shown; Step 3: The microprocessor ARM receives the preset abnormal alarm of the small chamber voltage and the impedance test or impedance patrol detection instruction from the PC side and sends them to the control module FPGA; After receiving the signal from the microprocessor ARM, the control module FPGA performs logical processing and applies an AC current excitation signal to the stack area where the voltage - abnormal small chamber is located or the preset stack area to be patrolled and measured through the AC current output module of the excitation module; Step 4: According to the open - circuit voltage of the small chamber collected in Step 2, while executing Step 3, 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, and outputs the corresponding DC voltage to the front end of the acquisition module; Step 5: The signal acquisition module processes and converts the voltage signals input in Step 1 and Step 4, and at the same time transmits the AC voltage component values (filtered AC voltage signals) collected at both ends of the sampling resistor and both ends of the small chamber of the stack to the signal analysis module DSP (i.e., the digital signal analysis and processing module in the figure) through the AC voltage acquisition module; Step 6: The signal analysis module DSP calculates the AC current by calculating the ratio of the AC voltage across the sampling resistor to the resistance in real time, and calculates the ratio of the AC voltage across the small chamber collected to the AC current, to obtain the AC impedance of the test small chamber; The signal transmission path in the above steps is as Figure 3 shown; Step 7: If the system is set to the inspection mode, after the impedance measurement of the cells in the selected stack inspection test area is completed, the microprocessor ARM will send a switching instruction to the control module FPGA according to the program settings of the inspection. The FPGA will process the instruction and control the electronic relay through the logic circuit to select and switch the output circuit of the alternating current output module, and then excite the electrolytic cell stack cells in the next stack inspection area. Then, the entire alternating current impedance inspection system repeats the operations in Steps 3 to 6 until the impedance measurements of all the electrolytic cell cells in the set stack inspection areas are completed.

[0037] In the above steps, the calculation process of the signal analysis module DSP includes: If in Step 3, the alternating current output module applies an alternating current excitation signal with a set frequency to the selected stack inspection test area (the stack area where the voltage-abnormal cell is located or the preset stack area to be inspected and measured), the test impedance value of the cells in the selected stack inspection test area can be calculated, and its calculation formula is: ; Wherein, is the impedance test value of the th cell in the selected stack inspection test, is the measured alternating voltage value of the th cell in the selected stack inspection test area, is the total excitation current output by the alternating current output module; If in Step 3, the alternating current output module applies an alternating current excitation signal with a scanning frequency to the selected stack inspection test area, then using the modulus of the alternating current impedance of the cell and the phase difference between the alternating voltage and the alternating current at different frequencies, the real part Zre and the imaginary part Zim of the alternating current impedance of the cell are calculated in real time, and its calculation formula is: ; ; Furthermore, the test impedance value of the cells or battery cores in the selected stack inspection test area is obtained, and its expression is: ; Wherein, is the real part of the impedance of the th cell or battery core in the selected stack inspection test area, is the imaginary part of the impedance of the th cell in the selected stack inspection test area.

[0038] Such as Figure 4As shown, when the number of cells in the stack is too large and the current is too high to perform an excitation test on the entire series-connected stack simultaneously, impedance tests and analyses are only carried out on the cells in the selected inspection test area of the stack. Therefore, the unselected part of the stack does not fall within the scope of testing and research, but it will form a parallel circuit with the area to be inspected and tested, and a power source or load is connected in series to this parallel circuit.

[0039] Therefore, when performing impedance tests, the total excitation current output by the AC current output module is , because the inspection test area and the non-test area form a parallel circuit, the current will be divided into flowing through the inspection test area and flowing through the non-test area; the AC voltage measurement of the cells in the area to be inspected and tested is , then its impedance calculation formula is , but in fact, the current collected by conventional instruments or test systems is the total excitation current , so the impedance calculated using the instrument is . Then there is a deviation between the true impedance value and the test impedance value, and the variation BR can be calculated using the following formula: ; Also because , since the potential of the parallel circuit is the same, , finally, we can get: ; where BR is the deviation rate between the true impedance value and the test impedance value; N is the total number of cells in the entire stack to be tested.

[0040] Or the deviation can also be expressed by the ratio of the test impedance value to the true impedance value, as shown in the following formula, ; where is the ratio of the test impedance value to the true impedance value, and the closer its value is to 1 (i.e., the smaller a / N is), the closer the test impedance value is to the true impedance value.

[0041] By replacing the cells with battery cells, the inspection test method described in this embodiment can also be used for impedance measurement of battery stacks, and its steps and calculation methods are the same as those in this embodiment, and the present invention will not be elaborated further.

[0042] As can be seen from the above formula, the more cells or battery cores in the tested stack and the fewer cells or battery cores in the inspection area, the closer the measured value of the instrument is to the true value. When the selected number of cells or battery cores for inspection is 2% of the total number of cells (for example, the number of cells or battery cores in the inspection area is 8 and the total number of cells or battery cores in the stack is 400), the measured value of the instrument is 98% of the true value. If the number of cells or battery cores inspected at this time is less than 4, the impedance deviation can be controlled to be less than 1%. It can be considered that the impedance value measured by the instrument is the true value or the measurement accuracy of the impedance value is relatively high, thus solving the problem that conventional instruments cannot measure or have a large deviation for high-power stacks with a large number of cells or battery cores and a large current.

[0043] If the influence brought by the power supply or load cannot be ignored either, the impedance characteristics of the power supply or load need to be considered. Since the power supply belongs to an AC / DC circuit, it can be regarded as a relatively large capacitor, for example ; there is also the following relationship: , Similarly, it can be calculated according to the equal voltage of the parallel circuit that ; Among them, is the angular frequency of the excitation current for impedance testing; is the capacitance value of the power supply or load.

[0044] As can be seen from the above analysis, the lower the frequency, the smaller the impedance of the power supply or load capacitance and the cells or battery cores, and the smaller the influence brought by the power supply or load and the unselected measurement area for inspection. Therefore, the AC impedance inspection and testing system and testing method involved in the present invention can fill the technical gap in the AC impedance testing of high-power stacks through the design of the system, and effectively solve problems such as high power, high cost, difficult explosion protection, and inaccurate data in the measurement, so as to be applied in the field of AC impedance testing of high-power stacks with a large number of cells or battery cores and a large current (the number of cells or battery cores exceeds 100 and the current exceeds 1000A).

[0045] The above has described the embodiments of the present invention. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Without departing from the scope and technical principles of the described embodiments, many modifications and changes are obvious to those of ordinary skill in the art in this technical field, and these modifications and changes should also be regarded as the protection scope of the present invention.

Claims

1. An AC impedance inspection test system for a battery stack, characterized in that: It includes a microprocessor, a control module, an excitation module, a signal acquisition module and a signal analysis module; The microprocessor is respectively connected to the PC and the control module for communication; The excitation module is in communication connection with the control module and is electrically connected with the battery stack to be tested, and is used to apply an AC excitation current signal and a DC bias voltage signal to the battery stack to be tested; The signal acquisition module is connected to the battery stack to be tested through a pre-isolation amplifier, and is used to collect the voltage signal of the battery stack to be tested and transmit it to the signal analysis module; The signal analysis module is in communication connection with the control module and the signal acquisition module, and transmits the calculated AC impedance data to the PC via the control module and the microprocessor.

2. The AC impedance inspection test system of the battery stack 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 of the control module, so as to switch the inspection and testing area of ​​the battery stack; The signal output module includes an AC current output module and a DC voltage output modules, where a is the number of channels that can measure cells or cells in the selected battery stack inspection test area; The AC current output module applies an AC excitation current signal to both ends of the battery stack in the selected battery stack inspection test area; The DC voltage output module applies a DC bias voltage signal to each cell or battery cell in the selected battery stack inspection test area.

3. The AC impedance inspection test system of the battery stack according to claim 1, characterized in that: It also includes a sampling resistor for converting the current signal into a voltage signal, wherein the sampling resistor is connected in series with the output circuit and is placed at the negative terminal of the output circuit; The signal acquisition module acquires the voltage signal of each small chamber or battery cell in the sampling resistor and the selected battery stack inspection test area; wherein the voltage signal of each small chamber or battery cell in the selected battery stack inspection test area is acquired through a pre-isolation amplifier.

4. The AC impedance inspection test system of the battery stack according to claim 3, characterized in that: The pre-isolation amplifier is connected to each cell or battery cell in the battery stack to be tested, collects the voltage at both ends of the cell or battery cell by magnetic coupling, and transmits it to the signal acquisition module after isolation and amplification processing; 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; wherein N is the total number of cells of the battery stack to be tested, the N DC voltage acquisition channel units are respectively used to acquire the DC voltages at both ends of the corresponding cells or cells, and 1 DC voltage acquisition channel unit is used to acquire the DC voltages at both ends of the sampling resistor; The AC voltage acquisition submodule includes N+1 AC voltage acquisition channel units, 1 AC voltage acquisition channel unit is used to acquire the AC voltage across the sampling resistor, and N AC voltage acquisition channel units are respectively used to acquire the AC voltage across the corresponding small chamber or battery cell, and a AC voltage acquisition channel units among the N AC voltage acquisition channel units are respectively used to acquire the AC voltage across each small chamber or battery cell in the selected battery stack inspection test area; wherein a is the number of channels that can measure the small chamber or battery cell in the selected battery stack inspection test area.

5. The AC impedance inspection test system for a large electrolytic cell stack according to claim 4, characterized in that: It also includes a low-pass filter for tracking and filtering the voltage signal collected by the pre-isolation amplifier and a gain amplifier for amplifying the voltage signal after filtering; the low-pass filter is connected to the signal collection module through the gain amplifier.

6. A method for testing AC impedance of a battery stack, based on the test system according to any one of claims 1 to 5, characterized in that: include: Step a: The signal acquisition module collects the initial voltage signals of all the cells or cells of the battery stack to be measured through the preamplifier and transmits them to the signal analysis module after processing. The signal analysis module processes the initial voltage signal of the signal acquisition module according to the control signal of the control module to obtain the open circuit voltage of all the cells or cells of the battery stack to be measured, and transmits the open circuit voltage to the PC through the control module and the microprocessor; Step b: The control module receives the command signal from the PC through the microprocessor, sends an excitation control signal to the excitation module in combination with the command signal and the open circuit voltage, and applies an AC excitation current signal and a DC bias voltage signal to the selected stack inspection test area through the excitation module; Step c: The signal acquisition module collects the voltage signal of the small chamber or the battery cell after excitation in the selected battery stack inspection test area through the preamplifier, and transmits it to the signal analysis module after processing; Step d: The signal analysis module calculates the AC impedance of the small room or battery cell in the selected battery stack inspection test area according to the signal transmitted by the signal acquisition module, and transmits it to the PC through the control module and the microprocessor; Repeat steps b to d until the impedance test of the cell or battery in the last inspection test area is completed.

7. The AC impedance inspection test method of a battery stack according to claim 6, characterized in that: The step of applying an excitation current signal and a voltage signal to the selected stack inspection test area through an excitation module includes: Apply an AC current signal to the selected battery stack inspection test area through an AC current output module; The corresponding DC voltage is outputted through the DC voltage output module to the front end of the acquisition module in the selected battery stack inspection test area.

8. The AC impedance inspection test method of a battery stack according to claim 6, characterized in that: The command signal on the PC side is an alarm for abnormal voltage in a cell or battery and an impedance test command or an impedance inspection command; the selected stack inspection test area is a stack inspection area where the excitation modules are started in sequence according to preset rules in the entire stack to be measured, or a stack inspection area where the abnormal voltage cell or battery is located.

9. The AC impedance inspection test method of a battery stack according to claim 6, characterized in that: The signal analysis module calculates the AC impedance of the cell or cell to be measured according to the signal transmitted by the signal acquisition module, including: If in step b, the AC current output module in the excitation module applies an AC current excitation signal of a set frequency to the selected battery stack inspection test area, the test impedance value of the cell or cell in the selected battery stack inspection test area is obtained, and the calculation formula is: ； in, Select the first The test impedance value of each cell or battery. Refers to the first The AC voltage measurement value of each cell or battery, It is the total excitation current output by the AC current output module.

10. The AC impedance inspection test method of a battery stack according to claim 9, characterized in that: The signal analysis module calculates the AC impedance of the cell or cell to be measured according to the signal transmitted by the signal acquisition module, and further includes: If in step b, the AC current output module in the excitation module applies an AC current excitation signal of a scanning frequency to the selected battery stack inspection test area, then the AC impedance modulus of the cell or cell is used The phase difference between AC voltage and AC current at different frequencies , calculate the real part Zre and imaginary part Zim of the AC impedance of the cell or battery in real time, and the calculation formula is: ； ； Then the test impedance value of the selected battery stack inspection test area chamber or battery cell is obtained, and its expression is: ； in, Select the stack inspection test area The real part of the impedance of a cell or battery, Select the stack inspection test area The imaginary part of the impedance of the chamber.

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