Fuel cell electrochemical impedance spectroscopy online detection system and method

Abstract

The application provides an on-line detection system and method for fuel cell electrochemical impedance, aiming at solving the problems of limited measurement frequency range and insufficient control precision caused by controller bandwidth limitation in the existing EIS on-line detection technology, comprising a power supply system of a fuel cell and a DC-DC converter, a disturbance signal generation module generating a sinusoidal disturbance current signal; a feedforward and feedback control module taking a total current reference signal as a control target and calculating a final adjustment duty cycle for driving the DC-DC converter; a data acquisition module synchronously acquiring an input voltage and an input current of the DC-DC converter as a response voltage signal and a response current signal when the DC-DC converter is driven by the final adjustment duty cycle; and an impedance demodulation module for demodulating and calculating the electrochemical impedance of the fuel cell based on the frequency of the response voltage signal, the response current signal and the sinusoidal disturbance current signal.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell electronic control technology, specifically relating to an online detection system and method for the electrochemical AC impedance of a fuel cell. Background Technology

[0002] Fuel cells are power generation devices that directly convert chemical energy into electrical energy. Due to their high efficiency, cleanliness, and environmental friendliness, they show broad application prospects in transportation, power supply, and other fields. To optimize the performance of fuel cell systems, diagnose their health status, and predict their lifespan, precise characterization of their internal electrochemical properties is necessary.

[0003] Electrochemical impedance spectroscopy (EIS) is a technique that measures the system response and analyzes the impedance change with frequency by applying a small-amplitude sinusoidal AC signal. EIS can effectively separate electrochemical processes at different time scales and can provide important evidence for the mechanism study, condition assessment and fault diagnosis of fuel cells.

[0004] Traditional EIS testing typically relies on expensive instruments such as dedicated electrochemical workstations to perform offline measurements of fuel cells in a laboratory environment. This approach is not only costly and requires large equipment, but also fails to reflect the dynamic characteristics of fuel cells under actual operating conditions in real time.

[0005] Existing technologies have also proposed schemes that combine disturbance injection with power conversion. For example, in a dual-closed-loop control architecture based on an outer voltage loop and an inner current loop, a sinusoidal disturbance is superimposed on the reference value of the current loop to achieve current excitation of the fuel cell. However, this scheme has several inherent technical drawbacks: (1) Low system integration: Traditional EIS systems are separate from the power supply system as independent peripherals, resulting in complex systems, high costs and large space occupation.

[0006] (2) Insufficient control accuracy: In traditional dual closed-loop control, the current inner loop PI controller cannot accurately track high-frequency sinusoidal disturbance signals. (3) Limited measurement frequency range: Due to the limitation of controller bandwidth, the measurement accuracy of traditional methods drops sharply in the frequency range above 1kHz.

[0007] (4) Poor system stability: Disturbance injection can easily cause system oscillations, affecting the normal operation of fuel cells. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides an online detection system and method for the electrochemical alternating impedance of fuel cells, aiming to solve the problems of limited measurement frequency range and insufficient control accuracy caused by controller bandwidth limitations in existing EIS online detection technologies.

[0009] To achieve the above objectives, the present invention provides: an online detection system for electrochemical AC impedance spectroscopy of a fuel cell, comprising: A power system comprising a fuel cell and a DC-DC converter, wherein the fuel cell is used to supply power and the DC-DC converter is used to convert the output of the fuel cell to the load side, characterized in that it further comprises: A disturbance signal generation module is used to generate a sinusoidal disturbance current signal and inject it into the DC-DC converter; The feedforward and feedback control module calculates the final adjustment duty cycle for driving the DC-DC converter based on the input and output voltages of the DC-DC converter and the total current reference signal obtained by combining the sinusoidal disturbance current signal. The data acquisition module is used to synchronously acquire the input voltage and input current of the DC-DC converter as response voltage signal and response current signal when the DC-DC converter is driven by the final adjusted duty cycle; An impedance demodulation module is used to demodulate and calculate the electrochemical AC impedance of the fuel cell based on the frequencies of the response voltage signal, the response current signal, and the sinusoidal perturbation current signal.

[0010] Furthermore, the DC-DC converter includes at least two parallel phase channels, each phase channel having an independent input current sampling unit, and the system having an input voltage sampling unit and an output voltage sampling unit.

[0011] Furthermore, the feedforward and feedback control module includes: A feedforward calculator is used to calculate the feedforward duty cycle based on the mathematical model of the DC-DC converter and real-time operating parameters. The feedback controller is used to calculate the feedback duty cycle based on the deviation between the disturbance current reference signal and the actual feedback current signal, wherein the disturbance current reference signal is obtained by distributing the total current reference signal to each phase of the multiphase parallel DC-DC converter; The weighted synthesis unit is used to assign weights to the feedback duty cycle and the feedforward duty cycle respectively, and generate the final adjustment duty cycle.

[0012] Furthermore, the feedback controller includes: The voltage outer loop PI controller is used to generate a voltage loop output based on the difference between the output reference voltage and the feedback voltage. The smaller unit is used to perform a smaller operation on the given current reference of the voltage loop output and the superimposed disturbance signal to obtain the total current reference signal; The inner current loop PI controller acquires the total current reference signal and distributes it to the inner current loop reference of each phase of the DC-DC converter. It generates a feedback duty cycle based on the difference between the inner current loop reference and the actual feedback current signal.

[0013] Furthermore, the impedance demodulation module uses digital demodulation technology based on quadrature reference signals. By constructing a unit quadrature reference signal, it obtains the real and imaginary parts of the response voltage signal and the response current signal, and uses low-pass filtering to suppress noise and obtain a stable estimate.

[0014] An online detection method for electrochemical AC impedance spectroscopy in fuel cells, characterized by comprising the following steps: A power system including a DC-DC converter is provided, the power system being powered by a fuel cell and used to convert the fuel cell output to the load side; Generate a sinusoidal disturbance current signal with a preset frequency and amplitude; Based on the input and output voltages of the DC-DC converter, and combined with the sinusoidal disturbance current signal, a disturbance current reference signal is generated for the power supply system to track. A combined feedforward and feedback control strategy is adopted to generate the final duty cycle signal driving the DC-DC converter; The final duty cycle signal is applied to the DC-DC converter to control the output voltage of the DC-DC converter; Simultaneously acquire the input voltage and input current signals of the DC-DC converter; Based on the acquired input voltage and current signals of the DC-DC converter, the electrochemical AC impedance of the fuel cell at the preset frequency is calculated using demodulation.

[0015] Furthermore, the feedforward and feedback composite control strategy is implemented as follows: The feedforward duty cycle is calculated based on the disturbance current reference signal and the state parameters of the power supply system. The feedback duty cycle is calculated based on the difference between the disturbance current reference signal and the feedback current. The feedforward duty cycle and the feedback duty cycle are combined according to weights to obtain the final duty cycle signal.

[0016] Furthermore, the feedforward duty cycle is obtained as follows: Based on the space-state averaging method, the inductor current state equation of the DC-DC converter is obtained as follows: in, For power inductors, Input voltage, For output voltage, Duty cycle; Transforming the inductor current equation yields the feedforward duty cycle. As shown in the following formula: In the formula, Indicates the total current reference signal The derivative with respect to time.

[0017] Furthermore, the disturbance current reference signal is obtained as follows: The generated sinusoidal disturbance current signal with a preset frequency and amplitude is represented as follows: Where A is the disturbance amplitude. The frequency of the disturbance angular frequency; Output reference voltage With feedback voltage After subtraction, the voltage loop output is obtained through a PI regulator. The voltage loop output is then compared with the given current reference signal superimposed with the disturbance signal, and the smaller value is taken to obtain the total current reference signal. , Total current reference signal Distributed to each phase of the multiphase parallel DC-DC converter, superimposed with sinusoidal disturbance current signal The disturbance current reference signal is obtained and expressed as: In the formula to These are the disturbance current reference signals for each phase. Here, n is the total current reference, and n is the number of phases in the DC-DC converter.

[0018] Furthermore, the final duty cycle signal is represented as follows: in, to These are the feedback duty cycles calculated based on the deviation between the disturbance current reference signal and the actual feedback current signal for each phase. The weights of the feedforward duty cycle, To provide feedback on the duty cycle weight, This refers to the feedforward duty cycle; Weight of feedforward duty cycle The weight of the feedback duty cycle Satisfies the following formula: In the formula Is the current perturbation frequency, Is the cut-off frequency, Monotonically increases with the increase of frequency; Dynamically adjust the weights of the feedforward duty cycle and the feedback duty cycle. When 0 < f < fc, < When f = fc, = 0.5; When f > fc, . Furthermore, the steps of demodulating and calculating the electrochemical AC impedance include: Construct a unit orthogonal reference signal with the same frequency as the sine perturbation current signal, including a sine reference signal and a cosine reference signal; Mix and low-pass filter the response voltage signal and the response current signal with the unit orthogonal reference signal respectively, and extract the amplitudes and phase angles of the response voltage signal and the response current signal; Calculate the impedance amplitude according to the amplitudes of the response voltage signal and the response current signal, The calculation formula of the impedance amplitude is: In the formula Is the calculated impedance amplitude, Is the amplitude of the input voltage after low-pass filtering, Is the amplitude of the input current after low-pass filtering; Calculate the impedance phase angle according to the phase angle. The calculation formula of the impedance phase angle is: In the formula Is the calculated impedance phase angle, Is the phase angle of the input voltage after low-pass filtering, Is the phase angle of the input current after low-pass filtering.

[0019] Furthermore, the steps of demodulating and calculating the electrochemical AC impedance are implemented by using the fast Fourier transform or the discrete Fourier transform algorithm.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The present invention embeds the EIS detection function into the fuel cell power system, without using expensive external electrochemical workstations or dedicated test equipment, realizes the high integration of the system, and can effectively reduce the hardware cost; This invention overcomes the bandwidth limitation of the feedback controller by introducing feedforward compensation based on the mathematical model of the DC-DC converter. The feedforward controller can predict and directly calculate the duty cycle required to track high-frequency sinusoidal signals. Even if the disturbance frequency far exceeds the bandwidth of the current loop PI, the system can still generate high-fidelity current disturbances, extending the upper limit of the measurable frequency of EIS to several kilohertz or even higher frequencies. The feedforward control is based on an accurate system model, which can predict system dynamics and perform feedforward compensation, solving the waveform distortion and phase lag problems caused by insufficient tracking capability of the PI controller, ensuring high fidelity of the injected signal and response signal, and significantly improving the accuracy of impedance measurement. This invention also dynamically adjusts the weights of the feedforward duty cycle and the feedback duty cycle, making full use of the robustness of feedback control in the low-frequency band and introducing feedforward control in the high-frequency band to share the control task, reducing the burden on the feedback controller, avoiding system oscillations that may be caused by over-adjustment of the PI controller at high frequencies, making the system highly robust to parameter changes and external disturbances, and enhancing the system stability during disturbance injection. Attached Figure Description

[0021] Figure 1 This is a block diagram of the online detection system for electrochemical AC impedance spectroscopy of fuel cells in an embodiment of the present invention; Figure 2 This is a schematic diagram of the power supply system in an embodiment of the present invention; Figure 3 This is a schematic diagram of the feedforward and feedback control module in an embodiment of the present invention; Figure 4 This is a schematic diagram of the steps of an online detection method for electrochemical AC impedance spectroscopy of a fuel cell according to an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of protection of the invention.

[0023] Reference Figure 1 , Figure 2 The online detection system for electrochemical AC impedance spectroscopy of fuel cells in this embodiment is built on a power supply system. The power supply system supplies power through fuel cell 1 and uses a multi-phase parallel BOOST type DC-DC converter 2 to convert the output of fuel cell 1 to the load side battery 3. The DC-DC converter has multiple parallel phase channels. By distributing the total power to multiple parallel units through the multi-phase parallel architecture, not only can the total power handling capacity and redundancy of the system be improved, but also the current ripple at the input of the converter can be effectively reduced through the interleaving control technology of each phase, providing a more stable working environment for the fuel cell. The system in implementation also includes the control of fuel cell output voltage. Sampling of the DC-DC converter output voltage The sampling includes independent sampling of the input current of each DC-DC converter. Voltage sampling can be performed using a resistor divider, while current sampling can be performed using a Hall current sensor, current transformer, or sampling resistor.

[0024] The online detection system for electrochemical AC impedance spectroscopy of fuel cells in the embodiment further includes: Disturbance signal generation module 4 is used to generate a sinusoidal disturbance current signal for injection into DC-DC converter 2; The feedforward and feedback control module 5 calculates the final adjustment duty cycle for driving the DC-DC converter 2 by using the total current reference signal obtained by combining the input voltage and output voltage of the DC-DC converter with the sinusoidal disturbance current signal as the control target. Data acquisition module 6 is used to synchronously acquire the input voltage and input current of the DC-DC converter as response voltage signal and response current signal when the DC-DC converter 2 is driven by the final adjusted duty cycle; Impedance demodulation module 7, connected to data acquisition module 6, is used to demodulate and calculate the electrochemical AC impedance of the fuel cell based on the frequency of the response voltage signal, response current signal, and sinusoidal disturbance current signal.

[0025] See Figure 3 In one embodiment of the present invention, the feedforward and feedback control module 5 includes: The feedforward calculator is used to calculate the feedforward duty cycle based on the mathematical model and real-time operating parameters of the DC-DC converter. The feedback controller is used to calculate the feedback duty cycle based on the deviation between the disturbance current reference signal and the actual feedback current signal. The disturbance current reference signal is obtained by distributing the total current reference signal to each phase of the multiphase parallel DC-DC converter. The weighted synthesis unit is used to assign weights to the feedback duty cycle and the feedforward duty cycle respectively, and generate the final adjustment duty cycle.

[0026] In this embodiment, the feedback controller includes: The voltage outer loop PI controller is used to generate a voltage loop output based on the difference between the output reference voltage and the feedback voltage. The smaller unit is used to perform a smaller operation on the given current reference of the voltage loop output and the superimposed disturbance signal to obtain the total current reference signal; The current inner loop PI controller acquires the total current reference signal and distributes it to the current inner loop reference of each phase of the DC-DC converter. It generates the feedback duty cycle based on the difference between the current inner loop reference and the actual feedback current signal.

[0027] In this embodiment, the impedance demodulation module 7 is based on the digital demodulation technology of orthogonal reference signals. By constructing a unit orthogonal reference signal, it obtains the real and imaginary parts of the response voltage signal and the response current signal, and uses low-pass filtering to suppress noise and obtain a stable estimate. In other embodiments of the present invention, the impedance demodulation module 7 can also use fast Fourier transform or discrete Fourier transform algorithms to calculate the electrochemical AC impedance.

[0028] The fuel cell electrochemical AC impedance spectroscopy online detection system of the embodiment utilizes only the original voltage and current sampling channels and PWM drive capability of the power supply system to achieve complete EIS online detection function with little or no increase in hardware cost. This greatly reduces the material cost of the system, simplifies system integration, and improves reliability.

[0029] See Figure 4 In an embodiment of the present invention, an online detection method for electrochemical AC impedance spectroscopy of a fuel cell is also provided. The method is based on a power system including a DC-DC converter, powered by the fuel cell, and used to convert the fuel cell output to the load side. The method includes the following steps: Step 1: Generate a sinusoidal disturbance current signal with a preset frequency and amplitude; Step 2: Based on the input and output voltages of the DC-DC converter, and combined with the sinusoidal disturbance current signal, generate a disturbance current reference signal for the power supply system to track. Step 3: Use a combined feedforward and feedback control strategy to generate the final duty cycle signal to drive the DC-DC converter; Step 4: Apply the final duty cycle signal to the DC-DC converter to control the output voltage of the DC-DC converter; Step 5: Synchronously acquire the input voltage and input current signals of the DC-DC converter; Step 6: Based on the collected input voltage signal and input current signal of the DC-DC converter, demodulate and calculate the electrochemical AC impedance of the fuel cell at the preset frequency.

[0030] In one specific embodiment of the present invention, step 3, the feedforward and feedback composite control strategy is executed as follows: The feedforward duty cycle is calculated based on the disturbance current reference signal and the state parameters of the power supply system. The feedback duty cycle is calculated based on the difference between the current reference signal with superimposed disturbance and the feedback current. The feedforward duty cycle and the feedback duty cycle are combined according to weights to obtain the final duty cycle signal.

[0031] In this embodiment, the feedforward duty cycle is obtained as follows: Based on the space-state averaging method, the inductor current state equation of the DC-DC converter is obtained as follows: in, For power inductors, Input voltage, For output voltage, Duty cycle; By transforming the inductor current equation, we can obtain the desired inductor current. Required duty cycle : In practical control, the desired inductor current in the above formula is... Using the disturbance current as a reference By substitution, the feedforward duty cycle can be obtained. As shown in the following formula: In the formula, Indicates the total current reference signal The derivative with respect to time; the feedforward duty cycle in the formula. It consists of two parts: The first part is the DC component, with a value of... This corresponds to the duty cycle required by the system at its steady-state operating point, and is used to maintain the stable operation of the system. The second part is the AC component, with a value of [value missing]. It provides real-time compensation for the dynamic effects caused by injected AC disturbances. The feedforward calculator can adaptively adjust parameters according to the real-time working status, improving the system's adaptability to changes in working conditions and ensuring measurement accuracy under different working conditions.

[0032] In this embodiment, the disturbance current reference signal is obtained as follows: The sinusoidal disturbance current signal with a preset frequency and amplitude generated in step 1 is represented as follows: Where A is the disturbance amplitude. Let ω be the angular frequency of the disturbance; it can be seen that the differential term of the disturbance signal includes the angular frequency. In traditional feedback control, the output of the PI controller is equivalent to the integral of the error signal, resulting in a 90° phase lag. Furthermore, the gain decreases as the frequency increases. In contrast, feedforward control directly calculates the differential term and predicts the trend of current change in advance, thereby eliminating phase lag and ensuring accurate tracking of high-frequency disturbance signals.

[0033] The outer voltage loop will output a reference voltage. With feedback voltage After differential calculation, the voltage loop output is obtained through a PI regulator. To prevent excessive current during dynamic processes, the inner current loop output is reduced by the given current reference of the voltage loop output and the superimposed disturbance signal to obtain the total current reference signal. It can protect fuel cells and power devices during transient processes such as system startup and sudden load changes.

[0034] Total current reference signal Distributed to each phase of the multiphase parallel DC-DC converter, superimposed with sinusoidal disturbance current signal The disturbance current reference signal is obtained and expressed as: In the formula to These are the disturbance current reference signals for each phase. Here, n is the total current reference, and n is the number of phases in the DC-DC converter. Then, the feedback duty cycle is calculated based on the deviation between the disturbance current reference signal and the actual feedback current signal Iin_fdbk.

[0035] The basic working principle of a DC-DC converter is as follows: When the switching transistor is turned on, the input power supply supplies power to the load through the power inductor, and the inductor stores energy at the same time; when the switching transistor is turned off, the inductor releases energy and supplies power to the load together with the input power supply. The output voltage can be adjusted by controlling the duty cycle of the switching transistor.

[0036] In this embodiment, the final duty cycle signal is represented as follows: in, to These are the feedback duty cycles calculated based on the deviation between the disturbance current reference signal and the actual feedback current signal for each phase. The weights of the feedforward duty cycle, To provide feedback on the duty cycle weight, This refers to the feedforward duty cycle; To fully leverage the advantages of feedforward control at high frequencies and the robustness of feedback control at low frequencies, this embodiment employs a dynamic weight adjustment scheme, where the weight of the feedforward duty cycle is adjusted accordingly. Weight of feedback duty cycle Satisfies the following formula: In the formula Is the current perturbation frequency, Is the cut-off frequency, Monotonically increases with the increase of frequency; when 0 < f < fc, < When f = fc, = 0.5; when f > fc, When the perturbation frequency Is much smaller than the cut-off frequency When, Approaches 0, Approaches 1. At this time, the final duty cycle is mainly determined by the feedback controller. In the low-frequency band, the PI controller can better track the reference signal, and the feedback control has robustness to model errors and external disturbances. Therefore, the feedback control is the main one. When the perturbation frequency Is close to or exceeds the cut-off frequency When, The value of increases, and the proportion of the feed-forward duty cycle in the final duty cycle increases and acts together with the feedback duty cycle; in the high-frequency band, the performance of the PI controller deteriorates, while the feed-forward control is based on an accurate model and can accurately predict high-frequency dynamics. Therefore, feed-forward compensation is introduced to ensure the tracking accuracy of high-frequency perturbations.

[0037] The traditional online EIS measurement method directly injects a sinusoidal current reference signal into the current-loop PI controller. However, due to the physical limitation of its own bandwidth, when the PI controller processes high-frequency signals, its gain will drop sharply and the phase will lag severely, resulting in that when the perturbation frequency exceeds the current-loop bandwidth, the actually generated inductor current cannot accurately track the given sinusoidal reference, and the injected current waveform will have serious amplitude attenuation and phase lag. In the embodiment, this problem is solved by introducing feed-forward compensation based on the mathematical model of the BOOST converter. The feed-forward duty cycle Is calculated according to the system state and the desired current change rate, bypasses the slow response link of the PI controller, and directly compensates the system. When injecting high-frequency perturbations, the desired current change rate will also change at high frequency. The feed-forward controller can calculate the duty cycle required to compensate this dynamics, and then combined with dynamic weight adjustment, it ensures that even when the perturbation frequency far exceeds the current-loop bandwidth, a high-fidelity current perturbation can still be generated, greatly expanding the upper limit of the measurable frequency of EIS and making it possible to obtain impedance information of the fuel cell in the high-frequency region; Furthermore, the feedforward compensation of this invention ensures high fidelity of the injected current waveform from the source by dynamically compensating for the inductor current. Since the control quantity is generated predictively rather than hysterically corrected, it can eliminate phase lag and waveform distortion caused by insufficient controller bandwidth, ensuring that the current excitation signal applied to the fuel cell is a pure sine wave. This ensures that the measured voltage response signal can truly reflect the linear impedance characteristics of the fuel cell at that frequency, providing high-quality raw data for subsequent accurate impedance calculations and ensuring the accuracy and reliability of the measurement.

[0038] In step 4 of the embodiment, the final duty cycle signal is applied to the DC-DC converter to control the output voltage of the DC-DC converter; In step 5 of the embodiment, the input voltage signal and input current signal of the DC-DC converter are acquired simultaneously.

[0039] In this embodiment, step 6, the demodulation calculation to obtain the electrochemical AC impedance, includes: Construct a unit orthogonal reference signal with the same frequency as the sinusoidal disturbance current signal, including a sinusoidal reference signal and a cosine reference signal; The response voltage signal and response current signal are mixed with a unit orthogonal reference signal and low-pass filtered respectively to extract the amplitude and phase angle of the response voltage signal and response current signal; The impedance amplitude is calculated based on the amplitudes of the response voltage signal and the response current signal. The formula for calculating the impedance amplitude is as follows: In the formula To calculate the impedance magnitude, This represents the input voltage amplitude after low-pass filtering. This represents the amplitude of the input current after low-pass filtering. The impedance phase angle is calculated based on the phase angle. The formula for calculating the impedance phase angle is: In the formula To calculate the impedance phase angle, The phase angle of the input voltage after low-pass filtering. The calculated frequency, impedance amplitude, and impedance phase angle of the input current after low-pass filtering are stored and can be used for subsequent analysis and modeling. After completing the entire frequency scan, Nyquist plots, Bode plots, etc., can be plotted, and parameters such as ohmic resistance, charge transfer resistance, double-layer capacitance, and diffusion impedance of the fuel cell can be extracted through equivalent circuit model fitting.

[0040] It should be noted that the method for calculating the electrochemical AC impedance is optional. As an alternative, other advanced signal processing strategies can be used, such as performing a Fast Fourier Transform (FFT) or Discrete Fourier Transform (DFT) on the acquired voltage and current time-domain signals to directly extract the voltage and current phasors at the perturbation frequency points in the frequency domain, and then calculating the complex impedance through complex division.

[0041] Furthermore, in embodiments of the present invention, before performing steps 1 to 6 of the above-described method for online detection of electrochemical AC impedance spectroscopy in fuel cells, the following may also be performed: Before starting the measurement, the system should be initialized and calibrated, including: Calibrate each voltage and current sampling channel to eliminate zero-point deviation and gain error, ensuring sampling accuracy; Set EIS measurement parameters, including: scan frequency range, disturbance amplitude at each frequency point, sampling time at each frequency point, and sampling frequency. Initialize controller parameters; set the initial operating point of the BOOST converter, including output voltage reference and total current reference.

[0042] Furthermore, during system operation, the model parameters in the feedforward calculator can be dynamically optimized based on the real-time operating status to improve the accuracy of the feedforward model. The adaptive adjustment strategy includes updating the feedforward model parameters according to changes in the disturbance current, that is, calculating the feedforward quantity in real time based on the disturbance current. The feedforward gain coefficient is adaptively adjusted according to changes in the operating point, i.e., the feedforward amount is dynamically adjusted according to the disturbance frequency. With feedback volume Weights.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An online detection system for electrochemical AC impedance spectroscopy of a fuel cell, comprising: A power system comprising a fuel cell and a DC-DC converter, wherein the fuel cell is used to supply power and the DC-DC converter is used to convert the output of the fuel cell to the load side, characterized in that it further comprises: A disturbance signal generation module is used to generate a sinusoidal disturbance current signal and inject it into the DC-DC converter; The feedforward and feedback control module calculates the final adjustment duty cycle for driving the DC-DC converter based on the input and output voltages of the DC-DC converter and the total current reference signal obtained by combining the sinusoidal disturbance current signal. The data acquisition module is used to synchronously acquire the input voltage and input current of the DC-DC converter as response voltage signal and response current signal when the DC-DC converter is driven by the final adjusted duty cycle; An impedance demodulation module is used to demodulate and calculate the electrochemical AC impedance of the fuel cell based on the frequencies of the response voltage signal, the response current signal, and the sinusoidal perturbation current signal. The feedforward and feedback control module includes: A feedforward calculator is used to calculate the feedforward duty cycle based on the mathematical model of the DC-DC converter and real-time operating parameters. The feedback controller is used to calculate the feedback duty cycle based on the deviation between the disturbance current reference signal and the actual feedback current signal. The disturbance current reference signal is obtained by distributing the total current reference signal to each phase of the multiphase parallel DC-DC converter. A weighted synthesis unit is used to assign weights to the feedback duty cycle and the feedforward duty cycle respectively, and generate the final adjustment duty cycle; The feedback controller includes: The voltage outer loop PI controller is used to generate a voltage loop output based on the difference between the output reference voltage and the feedback voltage. The smaller unit is used to perform a smaller operation on the given current reference of the voltage loop output and the superimposed disturbance signal to obtain the total current reference signal; The inner current loop PI controller acquires the total current reference signal and distributes it to the inner current loop reference of each phase of the DC-DC converter. It generates a feedback duty cycle based on the difference between the inner current loop reference and the actual feedback current signal.

2. The online detection system for electrochemical AC impedance spectroscopy of a fuel cell according to claim 1, characterized in that... The DC-DC converter includes at least two parallel phase channels, each phase channel has an independent input current sampling unit, and the system has an input voltage sampling unit and an output voltage sampling unit.

3. The online detection system for electrochemical AC impedance spectroscopy of a fuel cell according to claim 1, characterized in that... The impedance demodulation module is based on digital demodulation technology using orthogonal reference signals. By constructing a unit orthogonal reference signal, it obtains the real and imaginary parts of the response voltage signal and the response current signal, and uses low-pass filtering to suppress noise and obtain a stable estimate.

4. A method for online detection of electrochemical AC impedance spectroscopy in fuel cells, characterized in that, The online detection system for electrochemical AC impedance spectroscopy of fuel cells based on claim 1 includes the following steps: A power system including a DC-DC converter is provided, the power system being powered by a fuel cell and used to convert the fuel cell output to the load side; Generate a sinusoidal disturbance current signal with a preset frequency and amplitude; Based on the input and output voltages of the DC-DC converter, and combined with the sinusoidal disturbance current signal, a disturbance current reference signal is generated for the power supply system to track. A combined feedforward and feedback control strategy is adopted to generate the final duty cycle signal driving the DC-DC converter; The final duty cycle signal is applied to the DC-DC converter to control the output voltage of the DC-DC converter; Simultaneously acquire the input voltage and input current signals of the DC-DC converter; Based on the acquired input voltage and current signals of the DC-DC converter, the electrochemical AC impedance of the fuel cell at the preset frequency is calculated using demodulation.

5. The online detection method for electrochemical AC impedance spectroscopy of fuel cells according to claim 4, characterized in that, The feedforward and feedback combined control strategy is implemented as follows: The feedforward duty cycle is calculated based on the disturbance current reference signal and the state parameters of the power supply system. The feedback duty cycle is calculated based on the difference between the disturbance current reference signal and the feedback current. The feedforward duty cycle and the feedback duty cycle are combined according to weights to obtain the final duty cycle signal.

6. The online detection method for electrochemical AC impedance spectroscopy of fuel cells according to claim 5, characterized in that, The feedforward duty cycle is obtained as follows: Based on the space-state averaging method, the inductor current state equation of the DC-DC converter is obtained as follows: ； in, For power inductors, Input voltage, For output voltage, Duty cycle; Transforming the inductor current equation yields the feedforward duty cycle. As shown in the following formula: ； In the formula, Indicates the total current reference signal The derivative with respect to time.

7. The online detection method for electrochemical AC impedance spectroscopy of fuel cells according to claim 6, characterized in that, The disturbance current reference signal is obtained as follows: The generated sinusoidal disturbance current signal with a preset frequency and amplitude is represented as follows: ； Where A is the disturbance amplitude. The frequency of the disturbance angular frequency; Output reference voltage With feedback voltage After subtraction, the voltage loop output is obtained through a PI regulator. The voltage loop output is then compared with the given current reference signal superimposed with the disturbance signal, and the smaller value is taken to obtain the total current reference signal. , Total current reference signal Distributed to each phase of the multiphase parallel DC-DC converter, superimposed with a sinusoidal disturbance current signal The disturbance current reference signal is obtained and expressed as: ； In the formula to These are the disturbance current reference signals for each phase. Here, n is the total current reference, and n is the number of phases in the DC-DC converter.

8. The online detection method for electrochemical AC impedance spectroscopy of fuel cells according to claim 7, characterized in that, The final duty cycle signal is represented as follows: ； in, to These are the feedback duty cycles calculated based on the deviation between the disturbance current reference signal and the actual feedback current signal for each phase. The weights of the feedforward duty cycle, To provide feedback on the duty cycle weight, This represents the feedforward duty cycle.

9. The online detection method for electrochemical AC impedance spectroscopy of fuel cells according to claim 8, characterized in that, Weight of feedforward duty cycle Weight of feedback duty cycle Satisfy the following formula: ； where is the current disturbance frequency, is the cut-off frequency, monotonically increases with the increase of frequency; Dynamically adjust the weights of the feedforward duty cycle and the feedback duty cycle. When 0 < f < fc, < when f = fc, = 0.5; When f > fc, .

10. The online detection method for electrochemical AC impedance spectroscopy of fuel cells according to claim 4, characterized in that, The steps for demodulation calculation to obtain electrochemical impedance spectroscopy include: Construct a unit orthogonal reference signal with the same frequency as the sinusoidal disturbance current signal, including a sinusoidal reference signal and a cosine reference signal; The response voltage signal and response current signal are mixed and low-pass filtered with the unit orthogonal reference signal, respectively, to extract the amplitude and phase angle of the response voltage signal and response current signal; The impedance amplitude is calculated based on the amplitudes of the response voltage signal and the response current signal. The formula for calculating impedance amplitude is: ； In the formula To calculate the impedance magnitude, This represents the input voltage amplitude after low-pass filtering. This represents the amplitude of the input current after low-pass filtering. The impedance phase angle is calculated based on the phase angle. The formula for calculating the impedance phase angle is: ； In the formula To calculate the impedance phase angle, The phase angle of the input voltage after low-pass filtering. The phase angle of the input current after low-pass filtering.

11. The online detection method for electrochemical AC impedance spectroscopy of fuel cells according to claim 4, characterized in that, The step of demodulation calculation to obtain electrochemical AC impedance is implemented using a fast Fourier transform or discrete Fourier transform algorithm.

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