Fuel cell AC impedance detection circuit structure and method

Abstract

The invention discloses a fuel cell AC impedance detection circuit structure, and belongs to the technical field of electrochemical AC impedance detection. The circuit structure comprises a blocking capacitor, a high-pass filtering and noise filtering module, a protection circuit, an isolation amplifier and an instrument amplification circuit which are electrically connected in sequence, the blocking capacitor is used for extracting AC voltage signals of the fuel cell, the high-pass filtering and noise filtering module is composed of a current-limiting resistor, a first resistor and a noise filtering capacitor and realizes low-frequency filtering and noise suppression, the protection circuit is used for suppressing high-voltage overshoot and undershoot during power-on and power-off, and the isolation amplifier realizes high-low voltage isolation transmission. The instrument amplification circuit improves the signal measurement precision. The problems that in the prior art, an isolation amplifier is prone to being damaged due to overshoot / undershoot, and signal precision loss is large are solved, and the method has the advantages of being remarkable in overshoot suppression effect, high in measurement precision and high in adaptability and can be widely applied to hydrothermal management optimization, electric pile service life prediction, fault diagnosis and other scenes of a fuel cell system.

Description

Technical Field

[0001] This application relates to the field of electrochemical AC impedance detection technology, and in particular to a circuit structure and method for detecting AC impedance in fuel cells. Background Technology

[0002] Electrochemical impedance spectroscopy (EIS) is a widely used characterization technique in the field of electrochemistry. By measuring and analyzing electrochemical impedance spectra, it is possible to effectively separate the individual effects of factors such as mass transfer, drainage, contact conductivity, and heat dissipation on the fuel cell structure. Therefore, it is widely used in scenarios such as hydrothermal management optimization of fuel cell structure, shutdown purging control before cold start, stack lifetime prediction, and membrane dry / flood fault diagnosis, providing important technical basis for the optimized design and practical application of fuel cell structure.

[0003] In practical applications, the equivalent model of a fuel cell can be simplified to a series structure of resistor Rf and capacitor Cf. EIS detection requires first acquiring instantaneous AC voltage and current values, and then calculating the real part (resistive component) and imaginary part (reactant component) of the load impedance. The signal extraction process is typically as follows: Figure 4 As shown. A traditional AC voltage response signal extraction circuit (refer to utility model patent CN217543242U) is as follows: Figure 3 As shown, in this circuit, the DC blocking capacitor C1 is used to isolate the high voltage DC voltage so that the required AC signal can be obtained at the output terminal a; the resistor R1 and the DC blocking capacitor C1 form a high-pass filter to filter out low-frequency signals; the capacitor C2 is used to filter out interference noise in the AC signal; the isolated signal transmission is then achieved through the isolation amplifier, and the signal is then modulated by the differential operational amplifier to obtain the waveform that is suitable for MCU detection.

[0004] However, the aforementioned traditional detection circuit has significant drawbacks in practical applications: on the one hand, during the power-on and power-off process of the fuel cell stack, due to the coupling effect of the DC blocking capacitor C1, extremely high overshoot and undershoot voltages will be generated at point a of the output terminal (e.g., Figure 5The key waveform characteristics of a typical embodiment of AC impedance detection shown are as follows: when the stack voltage is 500V, the overshoot and undershoot voltages of point a (Va) can reach the same level, which can easily damage the subsequent isolation amplifier. In the prior art, a high-power TVS diode is usually connected in parallel across resistor R1 for overvoltage suppression. However, the junction capacitance of the high-power TVS diode is large, which will seriously affect the signal sampling accuracy and sampling bandwidth. On the other hand, traditional circuits use differential operational amplifiers and discrete components to form the signal processing circuit. Due to the differences in the manufacturing process of discrete components, their parameter accuracy and consistency are poor, and the noise suppression effect is limited. Furthermore, the signal amplitude after transmission through the isolation amplifier has been reduced, and further processing by the differential operational amplifier can easily cause signal accuracy loss, further affecting the accuracy of impedance detection. Summary of the Invention

[0005] To address the problems of existing fuel cell AC impedance detection circuits, such as "high voltage overshoot / undershoot at point a during power-on and power-off of the fuel cell stack, leading to damage to the isolation amplifier" and "poor noise suppression and significant signal accuracy loss in discrete component signal processing circuits," this invention provides a detection circuit structure and corresponding detection method that can effectively suppress voltage overshoot / undershoot while improving signal measurement accuracy. The technical solution is as follows: On the one hand, a fuel cell AC impedance detection circuit structure is provided, including: The DC blocking capacitor (C1) is used to extract the AC voltage signal from the fuel cell; A high-pass filter and noise filtering module, connected to the DC blocking capacitor (C1), includes a current-limiting resistor (R7), a first resistor (R1), and a noise filtering capacitor (C2). The DC blocking capacitor (C1), the current-limiting resistor (R7), and the first resistor (R1) constitute a high-pass filter stage, and the noise filtering capacitor (C2) is used to filter out interference noise in the AC signal. A protection circuit, connected to the output of the high-pass filter and noise filtering module, is used to suppress high voltage overshoot and undershoot generated when the input is powered on or off. An isolation amplifier (U1) is connected to the protection circuit at its input terminal to achieve isolated transmission of AC signals from the high-voltage side to the low-voltage side. The instrument amplifier circuit (U2) has its input terminal connected to the output terminal of the isolation amplifier (U1) and is used to amplify the AC signal after isolation transmission to improve measurement accuracy.

[0006] Optionally, the protection circuit includes: Upper clamping diode (D1) and lower clamping diode (D2), wherein the anode of the upper clamping diode (D1) is connected to the output terminal of the high-pass filter and noise filtering module; A positive support power supply (S1) and a negative support power supply (S2) are provided. The negative terminal of the positive support power supply (S1) is connected to the cathode of the upper clamping diode (D1), and the positive terminal of the negative support power supply (S2) is connected to the anode of the lower clamping diode (D2). The cathode of the lower clamping diode (D2) is connected to the output terminal of the high-pass filter and noise filtering module. An energy absorption circuit consists of at least two current-limiting resistors and at least one set of capacitors. The first end of the energy absorption circuit is connected to the cathode of the upper clamping diode (D1), and the second end of the energy absorption circuit is connected to the anode of the lower clamping diode (D2). The at least two current-limiting resistors include a first energy absorption resistor (R8) and a second energy absorption resistor (R9). The at least one set of capacitors includes a first capacitor group (C4-C6) and a second capacitor group (C7-C9). The first energy absorption resistor (R8) is connected in series between the cathode of the upper clamping diode (D1) and the first capacitor group (C4-C6). The second energy absorption resistor (R9) is connected in series between the anode of the lower clamping diode (D2) and the second capacitor group (C7-C9). The first capacitor group (C4-C6) and the second capacitor group (C7-C9) are connected in series or in parallel to absorb energy generated by overshoot and undershoot.

[0007] Optionally, the upper clamping diode (D1) and the lower clamping diode (D2) are semiconductor clamping devices. The conduction direction of the upper clamping diode (D1) is from the output terminal of the high-pass filter and noise filtering module to the positive support power supply (S1), and the conduction direction of the lower clamping diode (D2) is from the negative support power supply (S2) to the output terminal of the high-pass filter and noise filtering module.

[0008] Optionally, the energy absorption stage includes a second resistor (R8), a third resistor (R9), and an energy absorption capacitor bank; The energy absorption capacitor bank includes multiple capacitors (C4-C9) connected in series or in parallel. The second resistor (R8) is connected to the first terminal of the energy absorption capacitor bank, and the third resistor (R9) is connected to the second terminal of the energy absorption capacitor bank. The first terminal of the energy absorption capacitor bank is connected to the cathode of the upper clamping diode (D1), and the second terminal of the energy absorption capacitor bank is connected to the anode of the lower clamping diode (D2).

[0009] Optionally, the value of the DC blocking capacitor (C1) shall not exceed 10uF, and the value of the current limiting resistor (R7) shall not exceed 2kΩ.

[0010] Optionally, the cutoff frequency f of the high-pass filter stage satisfies f=1 / [2πC1(R7+R1)], and the cutoff frequency f is less than the frequency range of the AC signal to be detected.

[0011] Optionally, the instrumentation amplifier circuit (U2) is a 3-op-amp structure, including an amplification factor adjustment resistor (Rg), which is a programmable resistor. The instrumentation amplifier circuit (U2) also includes differential signal input terminals (+IN, -IN), positive and negative power supplies (+Vs, -Vs), a reference input terminal (REF), and a signal output terminal (OUT).

[0012] Optionally, the programmable resistor (Rg) is composed of at least two fixed resistors with different resistance values ​​connected in series with electronic switches and then connected in parallel. The electronic switches are connected to the MCU control unit, and the resistance value of the programmable resistor (Rg) is switched by controlling the opening and closing of the electronic switches through the MCU.

[0013] Optionally, the amplification factor of the isolation amplifier (U1) is less than 1; The common-mode rejection ratio (CMRR) of the instrumentation amplifier circuit (U2) is not less than 112dB, the input bias current is not greater than 500pA, the input offset voltage is not greater than 35uV, and the differential input impedance is not less than 100GΩ.

[0014] On the other hand, a method for detecting the AC impedance of a fuel cell is provided, employing the aforementioned fuel cell AC impedance detection circuit structure. The method includes: Step 1: The mixed signal output by the fuel cell is used to extract the AC voltage signal through the DC blocking capacitor (C1). The mixed signal includes a high voltage DC component and an AC impedance signal. Step 2: The AC voltage signal passes through the high-pass filter and the current-limiting resistor (R7) and the first resistor (R1) of the noise filtering module to filter out low-frequency components, and then passes through the noise filtering capacitor (C2) to filter out interference noise. Step 3: The protection circuit clamps the overshoot and undershoot voltage of the AC voltage signal processed in Step 2 within the allowable input range of the isolation amplifier (U1) through the upper clamping diode (D1), the lower clamping diode (D2) and the energy absorption circuit, and absorbs the overshoot and undershoot energy. Step 4: The isolation amplifier (U1) isolates and transmits the clamped AC signal from the high-voltage side to the low-voltage side. Step 5: The instrumentation amplifier circuit (U2) adjusts the amplification factor of the AC signal by controlling the programmable resistor (Rg) through the MCU according to the amplitude of the AC signal, so as to amplify the AC signal after isolation transmission with high precision. Step 6: Acquire the amplified AC voltage signal and the corresponding AC current signal, calculate the real and imaginary parts of the AC impedance of the fuel cell, and complete the AC impedance detection.

[0015] This invention discloses a circuit structure and detection method for AC impedance detection in fuel cells, relating to the field of electrochemical AC impedance detection technology. The circuit structure includes a DC blocking capacitor (C1), a high-pass filter and noise filtering module, a protection circuit, an isolation amplifier (U1), and an instrumentation amplifier circuit (U2) connected in sequence. The DC blocking capacitor (C1) extracts the AC voltage signal from the fuel cell. The high-pass filter and noise filtering module consists of a current-limiting resistor (R7), a first resistor (R1), and a noise-filtering capacitor (C2) to achieve low-frequency filtering and noise suppression. The protection circuit suppresses high-voltage overshoot and undershoot during power-on and power-off. The isolation amplifier (U1) achieves high- and low-voltage isolated transmission. The instrumentation amplifier circuit (U2) improves signal measurement accuracy. This invention solves the problems of isolation amplifiers being easily damaged by overshoot / undershoot and resulting in significant signal accuracy loss in existing technologies. It has advantages such as significant overshoot suppression, high measurement accuracy, and strong adaptability, and can be widely applied to scenarios such as hydrothermal management optimization, stack life prediction, and fault diagnosis in fuel cell systems. Attached Figure Description

[0016] Figure 1 A complete schematic diagram of the AC impedance detection circuit for a fuel cell according to the present invention is shown. Figure 2 This is a schematic diagram of the key waveform characteristics of the AC impedance detection circuit architecture of the present invention; Figure 3 Circuit diagram of a general embodiment for AC impedance detection; Figure 4 Here is a flowchart of the AC impedance detection signal; Figure 5 This is a schematic diagram of key waveform characteristics for a general embodiment of AC impedance detection. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0018] In this article, "multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0019] The fuel cell AC impedance detection circuit structure and detection method of the present invention can be implemented through various adaptable embodiments.

[0020] Example 1 (Architecture) In one implementation, corresponding Figure 1 A complete schematic diagram of the proposed fuel cell AC impedance detection circuit is shown below. Figure 1The circuit can be seen to be composed of DC blocking capacitor C1, high-pass filter and noise filtering module, protection circuit, isolation amplifier U1 and instrumentation amplifier circuit U2 connected in sequence.

[0021] In one example, the DC blocking capacitor C1 is a 15nF / 1kV specification, which meets the design requirement that the value of C1 does not exceed 10uF. It is used to extract the AC voltage signal from the mixed signal output by the fuel cell and isolate the high voltage DC component.

[0022] The high-pass filter and noise filtering module includes a current-limiting resistor R7, a first resistor R1, and a noise-filtering capacitor C2. In one example, R7 is 300Ω and R1 is 2MΩ. C1, R7, and R1 together form a high-pass filter. The noise-filtering capacitor C2 is configured according to the actual interference suppression requirements and is used to filter out high-frequency interference noise mixed in the AC signal.

[0023] Regarding the core constraint "cutoff frequency f = 1 / [2πC1(R7+R1)] and less than the signal frequency", substituting C1 = 15nF, R7 = 300Ω, and R1 = 2MΩ given in the example above, the calculation is as follows: R7 + R1 = 2000300Ω, denominator is The final cutoff frequency f ≈ 5.3Hz, while the frequency of the AC signal to be detected is designed to be no less than 10Hz (cutoff frequency), thus satisfying the requirement that "cutoff frequency is less than signal frequency". The function of this high-pass filter is... Figure 4 The signal extraction logic is consistent with that in the (AC impedance detection signal flowchart), from... Figure 4 It can be seen that the AC signal needs to be filtered before entering the subsequent stages to ensure signal purity.

[0024] The structural design of protection circuit 4 corresponds to Figure 1 The detailed layout of the protection circuit is shown, and it is connected to the output of the high-pass filter and noise filtering module. This protection circuit includes an upper clamping diode D1, a lower clamping diode D2, a positive support power supply S1, a negative support power supply S2, and an energy absorption stage.

[0025] The exemplary D1 and D2 are 1000V / 1A semiconductor clamping devices, with their conduction directions being from node a to S1 and from S2 to node a, respectively; the exemplary S1 uses a 3.3V DC power supply and S2 uses a -3.3V DC power supply.

[0026] In the energy absorption stage, it consists of a first energy absorption resistor R8, a second energy absorption resistor R9, a first capacitor group C4-C6, and a second capacitor group C7-C9. In the example, R8 and R9 are both 1kΩ, and C4-C9 are 10uF. R8 is connected in series between the cathode D1 and C4, and R9 is connected in series between the anode D2 and C7. C4-C6 and C7-C9 are initially connected in series, that is, they contain multiple capacitors connected in series or in parallel.

[0027] Combination Figure 2 A schematic diagram of the key waveform characteristics of the AC impedance detection circuit architecture proposed in this invention is shown when the fuel cell stack is powered on (corresponding to...). Figure 2 At time t1, the measured overshoot voltage at node a is approximately 4.2V, exceeding the sum of the voltage at S1 and the forward voltage drop across D1 (3.3V + 0.5V = 3.8V). D1 conducts, and the overshoot current flows through D1 and R8 into C4-C6 to charge and absorb energy. Va is clamped to 3.8V. The stack is then powered off (corresponding to...). Figure 2 At time t2), the undershoot voltage Va is below -3.8V, D2 conducts, C7-C9 discharge to release energy, and Va is clamped to -3.8V. Figure 2 It can be clearly seen that the sine wave Vpp of Va does not exceed 4.2V (i.e., does not exceed the device input voltage of 5V), which meets the ±5V input limit of U1 and effectively suppresses high voltage overshoot and undershoot.

[0028] In one implementation, the isolation amplifier U1 is designed with a gain of less than 1, using a scaling factor of 0.4. Figure 1 The position and function of U1 are to achieve isolated transmission from the high-voltage side to the low-voltage side, and to reduce the ±3.8V signal of Va to ±1.52V for output to U2.

[0029] In one implementation, the instrumentation amplifier circuit U2 adopts a 3-op-amp structure, from Figure 1 The connection relationships of the differential signal input terminals (+IN, -IN), reference input terminal (REF), and signal output terminal (OUT) of U2 can be seen. For example, if the common-mode rejection ratio is designed to be no less than 112dB, the input bias current is no more than 500pA, the input offset voltage is no more than 35uV, and the differential input impedance is no less than 100GΩ, then the output range is adapted to 0~3.3V.

[0030] During the testing process, from Figure 1 The complete chain of signal extraction, filtering, isolation, amplification, and calculation can be seen.

[0031] The first step is to extract the AC voltage signal from the mixed signal output by the fuel cell (including high-voltage DC and AC impedance signals) via C1; The second step is to filter out low-frequency components below 10Hz (matching the cutoff frequency of 5.3Hz) through R7 and R1, and then filter out high-frequency noise through C2; The third step is that the protection circuit limits the signal overshoot / undershoot to the allowable range of U1 input by clamping D1 and D2 and absorbing the energy of C4-C9 and R8 and R9. Fourth step, U1 isolates and transmits the clamped signal to the low-voltage side; Fifth step, U2 adjusts the amplification factor according to the signal amplitude; The sixth step involves the MCU acquiring the voltage and corresponding current signals, calculating the real and imaginary parts of the impedance, and completing the detection.

[0032] In another embodiment, an alternative implementation of the energy absorption stage is provided, using the same parameters as the example above (R8=R9=1kΩ, C4-C9=10uF / 25V, D1 / D2=1000V / 1A, S1=3.3V, S2=-3.3V), corresponding to... Figure 1 The layout of the energy absorption stage in the protection circuit is changed only by altering the capacitor bank connection method. C4-C6 and C7-C9 are connected in parallel, which complies with the limitation of capacitor banks being connected in series or in parallel.

[0033] Specifically, according to the example parameters, after parallel connection, the total capacity of C4-C6 reaches 30uF, the total capacity of C7-C9 reaches 30uF, and the charging time constant τ = R8 × C_total = 1kΩ × 30uF = 0.03s. Figure 2 The waveform characteristics show that after parallel connection, Va has a faster overshoot / undershoot clamping response and a smoother waveform, which can clamp Va to a safe range more quickly, making it suitable for high-voltage fuel cell stack scenarios.

[0034] Furthermore, regarding the amplification factor adjustment function of the instrument amplifier circuit, corresponding to... Figure 1 The connection structure of the instrumentation amplifier circuit U2 and the programmable resistor Rg, from Figure 1 The layout of the 3 operational amplifiers in U2 is clearly visible. Rg is connected in parallel between the gain adjustment pins of U2 and is connected to the MCU control unit.

[0035] U2 still uses a 3-op-amp structure. The amplification factor adjustment resistor Rg is limited. For example, it can be composed of two fixed resistors of 10kΩ and 100kΩ connected in series with an electronic switch (MOS transistor) and then connected in parallel. The electronic switch control terminal is connected to the MCU.

[0036] When U1 outputs a ±1.52V signal, the MCU controls the electronic switch corresponding to the 100kΩ resistor to close, the amplification factor of U2 is adjusted to about 1.1 times, and the output signal is ±1.67V. Then, a 1.65V bias is superimposed through the REF terminal, and finally the 0~3.3V adaptation signal is output. When U1 outputs a small signal of tens of mV, the MCU switches to a 10kΩ resistor to increase the amplification factor and improve the measurement accuracy. This realizes the characteristics of programmable resistor amplification factor adjustment and fixed resistor + electronic switch forming a programmable resistor.

[0037] Example 2 (Detection Method) Another implementation method, concerning the detection method, corresponds to... Figure 1 and Figure 2 .

[0038] First, the mixed signal output from the fuel cell is processed by C1=15nF / 1kV to extract the AC signal, and then the high-voltage DC signal is isolated (corresponding to...). Figure 1 (The function of C1 in the middle). Secondly, the AC signal is filtered by R7=300Ω and R1=2MΩ to remove low-frequency components below 5.3Hz, and then filtered by C2 to remove high-frequency noise (corresponding to...). Figure 1 (The function of the high-pass filter and noise reduction module) Next, the protection circuit clamps the overshoot / undershoot to ±3.8V through D1 and D2, and C4-C9 and R8=R9=1kΩ absorb the energy (corresponding to...). Figure 1 Medium protection circuit and Figure 2 (waveform effect) Then, U1 transmits the signal to U2 (corresponding to) with a scaling factor of 0.4. Figure 1 (Isolation function of U1) Then, the MCU controls the electronic switch of Rg according to the signal amplitude, adjusts the amplification factor of U2, and outputs a 0~3.3V signal (corresponding to...). Figure 1 (Magnification function of U2) Finally, the MCU synchronously acquires the voltage signal and the corresponding AC current signal, calculates the real and imaginary parts of the impedance, and completes the detection.

[0039] The above detection method achieves a deep fit between the circuit structure and the detection method.

[0040] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0041] Those skilled in the art will understand that all or part of the steps of the above embodiments can be implemented by hardware, or by a program instructing related hardware. The program can be stored in a computer-readable storage medium, such as a read-only memory, a disk, or an optical disk. The above descriptions are merely optional embodiments of this application and are not intended to limit the application. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A fuel cell AC impedance detection circuit structure, characterized by comprising: The application relates to a fuel cell voltage signal acquisition circuit. The fuel cell voltage signal acquisition circuit comprises a direct-current blocking capacitor (C1) for extracting an alternating voltage signal of a fuel cell; a high-pass filtering and noise filtering module connected with the direct-current blocking capacitor (C1) and comprising a current-limiting resistor (R7), a first resistor (R1) and a noise filtering capacitor (C2), wherein the direct-current blocking capacitor (C1), the current-limiting resistor (R7) and the first resistor (R1) constitute a high-pass filtering link, and the noise filtering capacitor (C2) is used for filtering out interference noises in the alternating signal; a protection circuit connected with an output end of the high-pass filtering and noise filtering module and used for inhibiting high-voltage overshoot and undershoot generated during input power-on and power-off; an isolation amplifier (U1) connected with the protection circuit and used for realizing isolated transmission of the alternating signal from a high-voltage side to a low-voltage side; an instrument amplification circuit (U2) with an input end connected with an output end of the isolation amplifier (U1) and used for amplifying the alternating signal after the isolated transmission and improving measurement accuracy. The protection circuit comprises:

2. The fuel cell AC impedance detection circuit structure according to claim 1, characterized by, an upper clamping diode (D1) and a lower clamping diode (D2), wherein an anode of the upper clamping diode (D1) is connected with an output end of the high-pass filtering and noise filtering module; a positive support power supply (S1) and a negative support power supply (S2), wherein a negative electrode of the positive support power supply (S1) is connected with a cathode of the upper clamping diode (D1), a positive electrode of the negative support power supply (S2) is connected with an anode of the lower clamping diode (D2), and a cathode of the lower clamping diode (D2) is connected with the output end of the high-pass filtering and noise filtering module; an energy absorption link composed of at least two current-limiting resistors and at least one capacitor group, wherein a first end of the energy absorption link is connected with the cathode of the upper clamping diode (D1), a second end of the energy absorption link is connected with the anode of the lower clamping diode (D2), the at least two current-limiting resistors comprise a first energy absorption resistor (R8) and a second energy absorption resistor (R9), the at least one capacitor group comprises a first capacitor group (C4-C6) and a second capacitor group (C7-C9), the first energy absorption resistor (R8) is connected in series between the cathode of the upper clamping diode (D1) and the first capacitor group (C4-C6), the second energy absorption resistor (R9) is connected in series between the anode of the lower clamping diode (D2) and the second capacitor group (C7-C9), and the first capacitor group (C4-C6) and the second capacitor group (C7-C9) are connected in series or in parallel and used for absorbing energy generated by overshoot and undershoot. The upper clamping diode (D1) and the lower clamping diode (D2) are semiconductor clamping devices, the conduction direction of the upper clamping diode (D1) is from the output end of the high-pass filtering and noise filtering module to the positive support power supply (S1), and the conduction direction of the lower clamping diode (D2) is from the negative support power supply (S2) to the output end of the high-pass filtering and noise filtering module.

3. The fuel cell AC impedance detection circuit structure according to claim 2, characterized by The energy absorption link comprises a second resistor (R8), a third resistor (R9) and an energy absorption capacitor group.

4. The fuel cell AC impedance detection circuit structure according to claim 2, characterized by ​ The energy absorption capacitor group comprises a plurality of series or parallel capacitors (C4-C9), the second resistor (R8) is connected with a first end of the energy absorption capacitor group, the third resistor (R9) is connected with a second end of the energy absorption capacitor group, the first end of the energy absorption capacitor group is connected with a cathode of the upper clamping diode (D1), and the second end of the energy absorption capacitor group is connected with an anode of the lower clamping diode (D2).

5. The fuel cell AC impedance detection circuit structure according to claim 1, characterized by, The value of the DC blocking capacitor (C1) is not more than 10uF, and the value of the current limiting resistor (R7) is not more than 2kΩ.

6. The fuel cell AC impedance detection circuit structure according to claim 1, characterized by The cut-off frequency f of the high-pass filter satisfies f=1 / [2πC1(R7+R1)], and the cut-off frequency f is less than the frequency range of the AC signal to be detected.

7. The fuel cell AC impedance sensing circuit structure according to claim 1, wherein The instrument amplifier circuit (U2) is a 3-operational amplifier structure, comprising an amplification multiple adjusting resistor (Rg), the amplification multiple adjusting resistor (Rg) is a programmable resistor, and the instrument amplifier circuit (U2) further comprises a differential signal input end (+IN, -IN), a positive and negative power supply (+Vs, -Vs), a reference input end (REF) and a signal output end (OUT).

8. The fuel cell AC impedance detection circuit structure according to claim 7, characterized by, The programmable resistor (Rg) is composed of at least two fixed resistors with different resistance values connected in series and then connected in parallel, and the electronic switches are connected with the MCU control unit, so that the resistance value of the programmable resistor (Rg) is switched by opening and closing the electronic switches.

9. The fuel cell AC impedance sensing circuit structure according to claim 1, wherein, The amplification multiple of the isolation amplifier (U1) is less than 1; The common-mode rejection ratio (CMRR) of the instrument amplifier circuit (U2) is not less than 112dB, the input bias current is not greater than 500pA, the input offset voltage is not greater than 35uV, and the differential input impedance is not less than 100GΩ.

10. A method of detecting an alternating current impedance of a fuel cell, characterized by, The fuel cell AC impedance detection circuit structure and the method of any one of claims 1-9 are adopted, and the method comprises: Step 1: The mixed signal output by the fuel cell extracts an AC voltage signal through a DC blocking capacitor (C1), and the mixed signal contains a high-voltage DC component and an AC impedance signal; Step 2: The AC voltage signal is filtered through a current limiting resistor (R7) and a first resistor (R1) of a high-pass filter and a noise filter module to remove low-frequency components, and then filtered through a noise filter capacitor (C2) to remove interference noise; Step 3: The protection circuit clamps the overshoot and undershoot voltage of the AC voltage signal processed in step 2 within the input allowable range of the isolation amplifier (U1) through the upper clamping diode (D1), the lower clamping diode (D2) and the energy absorption link, and absorbs the overshoot and undershoot energy; Step 4: The isolation amplifier (U1) isolates and transmits the clamped AC signal from the high-voltage side to the low-voltage side; Step 5: The instrument amplifier circuit (U2) adjusts the amplification multiple by controlling the programmable resistor (Rg) according to the amplitude of the AC signal to amplify the AC signal transmitted by the isolation with high precision; Step 6: The amplified AC voltage signal and the corresponding AC current signal are collected, the real part and the imaginary part of the fuel cell AC impedance are calculated, and the AC impedance detection is completed.

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