Fuel cell stack alternating current impedance detection method based on DC-DC topology

Abstract

The invention relates to the technical field of fuel cell online diagnosis and health management, and discloses a fuel cell stack alternating current impedance detection method based on DC-DC topology, which dynamically associates the real-time working conditions (Idc, T, RH and Zmin) of a stack with an impedance measurement process, realizes real-time optimization of excitation intensity, and fundamentally solves the contradiction between test damage and measurement accuracy. And predictive control based on impedance iteration: the excitation intensity of the next frequency point is guided by using the measurement result of the previous frequency point, so that the system can adapt to the dynamic response characteristics of the galvanic pile at different frequencies. And dual safety guarantee: a three-dimensional safety protection system is constructed in combination with a voltage disturbance upper limit based on working conditions and current amplitude calculation based on impedance. On the premise of safety, the maximum effective signal strength which can be achieved under the current condition is used all the time, and the high signal-to-noise ratio and high precision of full-band measurement are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of online diagnostics and health management technology for fuel cells, and in particular to an in-situ detection method for AC impedance of fuel cell stacks based on DC-DC converter topology that integrates an adaptive calibration mechanism, aiming to achieve wide-frequency-domain, high-precision, and non-destructive electrochemical impedance spectroscopy measurement. Background Technology

[0002] Although existing technologies have attempted to utilize DC-DC converters for impedance measurement, such as the Chinese invention patent application CN113823817A which discloses an impedance measurement and control device and method for an on-board fuel cell, this device includes a fuel cell stack, a DC-DC converter, a current sensor, a voltage monitoring device, and a controller. The DC-DC converter and the voltage monitoring device are connected via a signal synchronization line; the current sensor is located inside the DC-DC converter; each electrode of the voltage monitoring device is connected to the output terminal of a single cell in the fuel cell stack. The controller, during normal operation of the fuel cell stack, activates the DC-DC converter to send an AC excitation signal to the stack. After the current sensor reading stabilizes, it activates the voltage monitoring device to obtain the AC impedance of each single cell in the stack based on the voltage of each cell at the same time and the measured current, thereby controlling the operation of the fuel cell stack. This achieves the measurement and control of the impedance of each single cell in the fuel cell stack.

[0003] However, in existing technologies, the intensity (amplitude) of the excitation signal is usually a preset fixed value or manually adjusted by the operator, which has the following significant drawbacks: 1) Uncontrollable risks: Under vulnerable conditions such as low load, low temperature, or flooding of the fuel cell stack, a fixed, large excitation signal may lead to local overheating, membrane dehydration, or catalyst particle migration, causing irreversible performance damage. 2) Poor signal-to-noise ratio: Under high load or high conductivity conditions, an excessively small excitation signal will cause the response signal to be submerged in noise, resulting in decreased measurement accuracy. 3) Lack of intelligence: It is impossible to dynamically adjust the testing strategy according to the real-time "health status" and "operating conditions" of the fuel cell stack.

[0004] Therefore, developing an adaptive calibration mechanism that can automatically and dynamically optimize the AC excitation signal strength based on the real-time operating conditions of the fuel cell stack is key to achieving safe, accurate, and reliable online diagnostics of fuel cells. Summary of the Invention

[0005] The purpose of this invention is to provide a method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology, which can automatically and dynamically optimize the AC excitation signal strength according to the real-time operating conditions of the stack. This method provides at least one beneficial option or creates conditions to solve one or more technical problems existing in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] A method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology is implemented using a detection system comprising: a DC-DC converter, a microcontroller (MCU), a DDS signal generator, a synchronous acquisition module, an Ethernet module, and a host computer. The detection process includes the following steps: 1) The microcontroller (MCU) continuously acquires the real-time DC operating current I of the fuel cell stack through the DC current signal acquisition module. dc Meanwhile, the microcontroller connects to external sensors and acquires environmental parameters such as the fuel cell stack operating temperature (T) and inlet / outlet humidity (RH) through a synchronous signal acquisition module.

[0008] 2) At the lowest frequency point (e.g., 1Hz), after the first measurement is completed by applying the lowest excitation signal current of 0.5%I_rated, the microcontroller uses the voltage and current data obtained by the AC current signal acquisition module and the AC voltage signal acquisition module (preferably the high-speed acquisition module ADS8412) to calculate the preliminary impedance modulus |Zlow| at that point using the least squares method.

[0009] 3) The microcontroller determines the operating current I based on the current. dc The maximum allowable voltage disturbance value ΔVmax is calculated using the formula based on the operating temperature T, inlet and outlet humidity RH, and initial impedance modulus |Zlow|.

[0010] ΔVmax=V_base×f_I(I dc )×f_T(T)×f_RH(RH_in,RH_out)×f_dRH(RH_out,RH_in)× f_Z(∣Zlow∣).

[0011] V_base = k_base × OCV, where k_base is usually taken as 0.01-0.02, and OCV is the open-circuit voltage.

[0012] f_I(I dc =I_rated / (I dc +0.1×I_rated). I_rated is the rated current of the fuel cell stack.

[0013] f_T(T)=max(0,min(1,(T-T_min) / (T_max-T_min)); T_min=60℃, T_max=90℃.

[0014] f_RH(RH_in,RH_out)=[(w_in×RH_in+w_out×RH_out) / 100]^n;w_in=0.6, w_out=0.4, n=1.5-2.0, RH_in is the inlet humidity of the fuel cell stack, and RH_out is the outlet humidity of the fuel cell stack.

[0015] f_dRH(RH_out,RH_in)=exp(-k×∣RH_out-RH_in∣ / 100), k=2.0, reflecting the balance of water management.

[0016] f_Z(|Zlow|) is a coefficient determined based on the ratio of the real-time measured low-frequency impedance amplitude (|Z_low|) to the reference impedance (Z_ref).

[0017] The low-frequency impedance amplitude measured in real time is included in the safety assessment; Z_ref: reference impedance (low-frequency impedance of a healthy fuel cell under rated operating conditions).

[0018] If |Z_low| < 0.7 × Z_ref, then f_Z = 1.2, indicating that the impedance is very small, the stack condition is excellent, and the amplitude range of the excitation signal can be appropriately widened.

[0019] If 0.7×Z_ref≤|Z_low|≤1.3×Z_ref, then f_Z=1.0 / (|Z_low| / Z_ref)β, indicating that the impedance is at normal attenuation, and β=0.5-1.

[0020] If 1.3×Z_ref<|Z_low|≤2.0×Z_ref, then f_Z=0.7, indicating that the impedance has increased significantly, strictly limiting the amplitude range of the excitation signal.

[0021] If |Z_low|>2.0×Z_ref, then f_Z=0.3, indicating that the fuel cell stack is severely degraded and the excitation signal is controlled to minimize disturbance.

[0022] 4) For each subsequent frequency point to be measured, the microcontroller uses the impedance modulus |Z| measured at the previous frequency point. prev | and the current ΔVmax, dynamically calculate the optimal AC excitation current amplitude I at this frequency point. ac _target.

[0023] I ac _target=ΔVmax / |Z prev |

[0024] 5) The MCU will calculate the optimal AC excitation current amplitude I at this frequency point. acThe target value is converted into a 12-bit amplitude control word for the DDS signal generator (using the AD9852 chip). The new amplitude control word is written to the AD9852 DDS signal generator via the SPI interface, and a refresh signal (rising edge of the upclock) is sent. The AC excitation signal generated by the DDS signal generator is processed sequentially by an amplifier circuit, a filter circuit, and a power operational amplifier module before being output to the fuel cell stack. The detection system then performs formal measurements and data acquisition at this frequency point with the new, optimized excitation intensity. The acquired new impedance data |Z current | Calculate the optimal AC excitation current amplitude I at the next frequency point ac The input to _target forms a dynamic closed-loop feedback system.

[0025] 7) The signal-to-noise ratio (SNR) of the acquired signals monitored by the control system. If the SNR is lower than a preset threshold (e.g., 40dB), and the current AC excitation current I... ac Still less than a "maximum safe amplitude" (composed of ΔVmax and minimum impedance Z). min Decision, I ac ≤ΔVmax / ∣Z min ∣), then I can be appropriately increased. ac To improve measurement quality, but still subject to ΔVmax constraints.

[0026] 8) If a sudden change in DC current, abnormal temperature, or drastic fluctuation in phase difference is detected during the measurement process, the system will immediately stop frequency sweeping, return the excitation signal to zero, and send an alarm to the host computer.

[0027] The technical solution provided by this invention has at least the following technical effects or advantages.

[0028] I. Pioneering Closed-Loop Adaptive Calibration Mechanism: For the first time, the real-time operating conditions of the fuel cell stack (I...) are integrated into the calibration mechanism. dc T, RH, |Z min |) It is dynamically linked to the impedance measurement process to achieve real-time optimization of the excitation intensity, fundamentally solving the contradiction between "test damage" and "measurement accuracy".

[0029] Second, it realizes predictive control based on impedance iteration: it uses the measurement results of the previous frequency point to guide the excitation intensity of the next frequency point, so that the system can adapt to the dynamic response characteristics of the fuel cell stack at different frequencies.

[0030] III. Dual Safety Guarantee: Combining "voltage disturbance limit based on operating conditions" and "current amplitude calculation based on impedance", a three-dimensional safety protection system is constructed.

[0031] Fourth, it can be seamlessly integrated into the DC-DC platform: the mechanism is fully implemented on the existing embedded hardware platform without the need to add extra complex equipment, which enhances the practical value of the system.

[0032] V. This invention effectively prevents fuel cell performance degradation or permanent damage caused by excessive excitation signals, and is particularly suitable for online health monitoring scenarios. Under safe conditions, it consistently uses the maximum effective signal strength achievable under current conditions, ensuring high signal-to-noise ratio and high accuracy across the entire frequency band. The system can autonomously "sense, decide, and execute," handling various complex operating conditions without human intervention. Through non-destructive diagnostics, potential faults can be detected earlier, guiding maintenance and extending the stack's lifespan. This lays a key technological foundation for achieving true "predictive health management" of fuel cell systems.

[0033] Other beneficial effects or technical advantages of the present invention will become more apparent in the following description or practice. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of the AC impedance detection system for a fuel cell stack provided in an embodiment of the present invention. Detailed Implementation

[0035] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings, making the technical solution and beneficial effects of the present invention clearer and more explicit. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products, and all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0036] Additional aspects and advantages of the invention will become apparent in the following description or may be learned by practice of the invention. Example 1

[0037] A method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology is disclosed. This method is implemented using a detection system comprising a microcontroller (MCU), a DDS signal generator, and a synchronous acquisition module connected to the MCU. The MCU, DDS signal generator, and synchronous acquisition module together form a DC-DC converter. The synchronous acquisition module acquires the operating signals of the fuel cell stack. The MCU generates a corresponding amplitude control word based on the acquired operating signals and outputs it to the DDS signal generator. The DDS signal generator then generates a corresponding AC excitation signal and outputs it to the fuel cell stack for AC impedance detection. The detection system also includes a host computer connected to the MCU via an Ethernet module for remote monitoring.

[0038] In this embodiment, the preferred fuel cell stack has a power of 100kW, a rated current of 400A, an OCV (open circuit voltage) of 350V, and Z_ref = 0.05Ω. According to the appendix... Figure 1 The system shown is an AC impedance detection system for a fuel cell stack based on a DC-DC topology. At the lowest frequency point of 1Hz, a minimum excitation signal current of 2A is applied. The current output current I of the fuel cell stack is acquired via a synchronous acquisition module. dc Operating temperature T and inlet / outlet humidity RH_in, RH_out, I dc= 300A, T=75℃, RH_in=80%RH, RH_out=95%RH, the microcontroller (MCU) synchronously calculates the preliminary impedance modulus |Z based on the above parameters. min |=0.05Ω, V_base=k_base×OCV=0.015×350=5.25V, f_I(Idc)=400 / (300+0.1×400)=400 / 340≈1.176, f_T(T)=(75-60) / (90-60)=0.5, f_RH=[(0.6×80+0.4×95) / 100]^1.5=(86 / 100)^1.5≈0.798、f_dRH=exp(-2×|95-80| / 100)=e^(-0.3)≈0.741、|Zlow|=Z_ref,f_Z=1.0、ΔVmax=5.25×1.176×0.5×0.798×0.741×1.0≈1.83V; set the next frequency point as |Zprev|=0.05Ω.

[0039] Microcontroller (MCU) uses formula I acThe new excitation current is calculated as _target = ΔVmax / |Zprev|, where Iac_target = ΔVmax / |Zprev| = 1.83 / 0.05 ≈ 36.6 A. This new excitation current is then applied at the next frequency point. All the above steps are repeated to achieve adaptive calibration that dynamically optimizes the AC excitation signal strength.

[0040] Safety Constraints: If the calculated Iac_target exceeds the stack's tolerance range ("maximum safe amplitude"), the system automatically limits it to ΔVmax / |Zmin| (|Zmin|=0.05Ω, then the upper limit is 1.83 / 0.05=36.6A). Failure Protection: Any abnormal parameter (such as T>90℃ or |Zlow|>2×Z_ref) triggers shutdown protection. Example 2

[0041] A method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology is provided, which is implemented using the same detection system as in Example 1.

[0042] In this embodiment, the fuel cell stack has a power of 100kW, a rated current of 380A, an OCV of 320V, and Z_ref=0.06Ω. The AC impedance detection method is as follows: at the lowest frequency point of 1Hz, a minimum excitation signal current of 1.9A is applied. The current fuel cell stack output current Idc, operating temperature T, and inlet and outlet humidity RH_in and RH_out are collected through a synchronous acquisition module, where Idc=250A, T=70℃, RH_in=75%RH, and RH_out=90%RH. Based on the above parameters, the microcontroller (MCU) synchronously calculates the preliminary impedance modulus |Zmin|=0.072Ω, V_base=0.015×320=4.8V, f_I(Idc)=380 / (250+0.1×380)=380 / 288≈1.319, f_T(T)=(70-60) / (90-60)=0.333, and f_RH=[(0.6×75+0.4×9 The formula is: f_dRH = exp(-2×|90-75| / 100) = e^(-0.3) ≈ 0.741, |Zlow| = 0.072Ω = (1.2×Z_ref), f_Z = 1.0, ΔVmax = 4.8×1.319×0.333×0.729×0.741×1 ≈ 1.139V. The microcontroller (MCU) calculates the new excitation current using the formula Iac_target = ΔVmax / |Zprev|, which is approximately 15.8A. The new excitation current is then applied at the next frequency point. All the above steps are repeated to achieve adaptive calibration of the AC excitation signal strength.

[0043] Safety Constraints: If the calculated Iac_target exceeds the stack's tolerance range ("maximum safe amplitude"), the system automatically limits it to ΔVmax / |Zmin| (|Zmin|=0.05Ω, then the upper limit is 1.139 / 0.072=15.8A). Failure Protection: Any abnormal parameter (such as T>90℃ or |Zlow|>2×Z_ref) triggers shutdown protection.

[0044] It should be noted that any process or method described in the flowcharts or otherwise herein in this specification can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order according to the functions involved, as should be understood by those skilled in the art to which the embodiments of the invention pertain.

[0045] It should be understood that various parts of the present invention can be implemented using hardware, software, firmware, or a combination thereof. Those skilled in the art will understand that all or part of the steps of the methods described in the above embodiments can be implemented by a program instructing related hardware, and the program can be stored in a computer-readable storage medium. When executed, the program includes one or a combination of the steps of the method embodiments.

[0046] It should be understood that although embodiments of the present invention have been shown and described above, these embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention. Improvements and substitutions based on the present invention using techniques known in the art all fall within the protection scope of the present invention, which should be defined by the claims and their equivalents. Parts not described in the specific embodiments are all prior art or common knowledge.

Claims

1. A method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology, characterized in that, The detection system is based on the following detection system, which includes a microcontroller, a DDS signal generator and a synchronous acquisition module connected to the microcontroller. The microcontroller, the DDS signal generator and the synchronous acquisition module together form a DC-DC converter. The synchronous acquisition module is used to acquire the operating signals of the fuel cell stack. The microcontroller (MCU) generates a corresponding amplitude control word based on the acquired operating signals and outputs it to the DDS signal generator. The DDS signal generator generates a corresponding AC excitation signal and outputs it to the fuel cell stack to perform AC impedance detection of the fuel cell stack. The testing process includes the following steps: 1) The microcontroller continuously acquires the real-time DC operating current I of the fuel cell stack through the synchronous signal acquisition module. dc The fuel cell stack operating temperature T, fuel cell stack inlet humidity RH_in, and fuel cell stack outlet humidity RH_out; 2) At the lowest frequency point, after the first measurement is completed with the lowest excitation signal current of 0.5%I_rated, the microcontroller uses the voltage and current data obtained by the synchronous signal acquisition module to calculate the preliminary impedance modulus |Zlow| at that point using the least squares method; I_rated is the rated current of the fuel cell stack. 3) The microcontroller determines the operating current I based on the current. dc The maximum allowable voltage disturbance value Δvmax is calculated using the formula based on the operating temperature T, the inlet humidity RH_in of the fuel cell stack, the outlet humidity RH_out of the fuel cell stack, and the initial impedance modulus |Zlow|. ΔVmax=V_base×f_I(I dc )×f_T(T)×f_RH(RH_in,RH_out)×f_dRH(RH_out,RH_in)×f_(∣Zlow∣); V_base = k_base × OCV, where k_base is usually taken as 0.01-0.02, and OCV is the open-circuit voltage; f_I(I dc )=I_rated / (I dc +0.1×I_rated); f_T(T)=max(0,min(1,(T-T_min) / (T_max-T_min)); T_min=60℃, T_max=90℃; f_RH(RH_in,RH_out)=[(w_in×RH_in+w_out×RH_out) / 100]^n;w_in=0.6, w_out=0.4, n=1.5-2.0, RH_in is the inlet humidity of the fuel cell stack, and RH_out is the outlet humidity of the fuel cell stack; f_dRH(RH_out,RH_in)=exp(-k×|RH_out-RH_in| / 100), k=2.0, reflecting the balance of water management; 4) For each subsequent frequency point to be measured, the microcontroller uses the impedance modulus |Z| measured at the previous frequency point. prev | and the current ΔVmax, dynamically calculate the optimal AC excitation current amplitude I at this frequency point. ac _target; I ac _target=ΔVmax / ∣Z prev ∣; 5) The microcontroller will calculate the optimal AC excitation current amplitude I at this frequency point. ac _target is converted into a 12-bit amplitude control word for the DDS signal generator; the new amplitude control word is written to the signal generator via the SPI interface and a refresh signal is sent; the detection system then performs formal measurement and data acquisition at this frequency point with the new, optimized excitation intensity; the acquired new impedance data |Z current | Calculate the optimal AC excitation current amplitude I at the next frequency point ac The input to _target forms a dynamic closed-loop feedback system.

2. The method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology according to claim 1, characterized in that, The low-frequency impedance amplitude measured in real time is included in the safety assessment. If |Z_low| < 0.7 × Z_ref, then f_Z(|Zlow|) = 1.2, indicating that the impedance is very small and the stack condition is excellent; it can widen the amplitude range of the excitation signal. If 0.7×Z_ref≤|Z_low|≤1.3×Z_ref, then f_Z(|Zlow|)=1.0 / (|Z_low| / Z_ref)β, indicating that the impedance is at normal attenuation, β=0.5-1; If 1.3×Z_ref<|Z_low|≤2.0×Z_ref, then f_Z(|Zlow|)=0.7, indicating that the impedance has increased significantly and the amplitude range of the excitation signal needs to be strictly limited. If |Z_low|>2.0×Z_ref, then f_Z(|Zlow|)=0.3, indicating that the fuel cell stack is severely degraded and the excitation signal needs to be controlled to minimize disturbance; Z_ref is the reference impedance.

3. The method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology according to claim 1, characterized in that, The control system monitors the signal-to-noise ratio (SNR) of the acquired signals; if the SNR is lower than a preset threshold, and the current AC excitation current I... ac If it is still less than a maximum safe amplitude, then increase I within the maximum safe amplitude range. ac .

4. The method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology according to claim 3, characterized in that, The preset threshold is 30-50dB.

5. The method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology according to claim 3, characterized in that, The method for determining the maximum safe amplitude is I. ac ≤ΔVmax / ∣Z min | 6. The method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology according to claim 1, characterized in that, The detection system also includes a host computer, which is connected to the microcontroller (MCU) via an Ethernet module for remote monitoring. If a sudden change in DC current, abnormal temperature, or drastic fluctuation in phase difference is detected during the measurement process, the system immediately stops frequency sweeping, returns the excitation signal to zero, and sends an alarm to the host computer.

7. The method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology according to claim 1, characterized in that, The synchronization signal acquisition module includes a DC current signal acquisition module, an AC current signal acquisition module, and an AC voltage signal acquisition module.

8. The method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology according to claim 1, characterized in that, The synchronization signal acquisition module includes an ADS8412 module.

9. The method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology according to claim 1, characterized in that, The lowest frequency point is 1-2Hz.

10. The method for detecting the AC impedance of a fuel cell stack based on a DC-DC topology according to claim 1, characterized in that, The DDS signal generator is an AD9852 module. The AC excitation signal generated by the DDS signal generator is processed sequentially by an amplification circuit, a filtering circuit, and a power operational amplifier module before being output to the fuel cell stack.

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