Battery internal resistance state monitoring method based on voltage pulse method

Abstract

The invention discloses a battery internal resistance state monitoring method based on a voltage pulse method, and relates to the technical field of battery detection, and the method comprises the steps: carrying out the current excitation of a battery pack in a frequency sweeping mode; sending the collected battery data to an upper computer to wait for data processing; the upper computer performs data error verification and data preprocessing on the received data; monitoring the characteristic parameters of the internal resistance of each single battery in real time; drawing and displaying an electrochemical impedance spectrogram of the internal resistance of each single battery; performing curve fitting on the electrochemical impedance spectrogram of the internal resistance of the single battery; calculating model parameters of the equivalent circuit model of the battery pack; and monitoring and diagnosing the health state of the battery pack by using a linear discriminant analysis method. Important characteristic parameters of the cell are monitored on line, so that the health state of the fuel cell is monitored and diagnosed, and the service life is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of battery detection, and in particular to a method for monitoring the internal resistance state of a battery based on a voltage pulse method. Background Art

[0002] With the rapid development of the world economy, energy shortage, environmental pollution and climate change are becoming increasingly prominent. These problems have become the three major challenges facing the development of human society today. Fuel cells are devices that directly and continuously convert the chemical energy of externally supplied fuel and oxidant into electrical energy through electrochemical reactions without combustion. They have the advantages of high energy efficiency and low environmental pollution, and have become the most promising new energy source that has attracted widespread attention.

[0003] Existing methods such as CN113671398B - A real-time monitoring device for battery internal resistance and its monitoring method are relatively simple in terms of data processing and analysis, and use a health status calculation formula to evaluate the health status of the battery pack. However, this formula relies on the internal resistance at the end of the battery life and the initial internal resistance when the battery is just put into operation. The accuracy of these two parameters is crucial for the assessment of the health status. However, in practical applications, it may be difficult to accurately obtain these two parameters because they will be affected by various interference factors, thereby affecting the reliability of the health status assessment. This paper adopts the method of establishing a linear discriminant function based on sample data and fault categories, and linearly discriminates the operating data of the battery to be tested with the operating data in the historical database, so as to realize fuel cell health status monitoring and fault type diagnosis, and extend the service life. Summary of the invention

[0004] In order to solve the above technical problems, a battery internal resistance state monitoring method based on a voltage pulse method is provided. This technical solution solves the problems raised in the above background technology.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A battery internal resistance state monitoring method based on a voltage pulse method, wherein a programmable AC power supply generates a voltage pulse of corresponding amplitude and frequency under the control of preset amplitude and frequency parameters, and current excitation is performed on the battery pack in a frequency sweeping manner through a DC isolation capacitor;

[0007] Complete the data collection of each single battery in the battery pack, and send the collected battery data to the host computer for data processing;

[0008] The host computer performs data error checking and data preprocessing on the received data;

[0009] Real-time monitoring of characteristic parameters of the internal resistance of each single-chip battery, wherein the characteristic parameters include impedance amplitude, impedance real part and impedance imaginary part;

[0010] Based on the characteristic parameters of the internal resistance of each single-chip battery, draw and display the electrochemical impedance spectrum of the internal resistance of each single-chip battery;

[0011] Perform curve fitting on the electrochemical impedance spectrum of the internal resistance of a single cell;

[0012] Calculating model parameters of an equivalent circuit model of a battery pack, wherein the model parameters include ohmic impedance, polarization impedance, and diffusion impedance;

[0013] Linear discriminant analysis is used to monitor and diagnose the health status of battery packs.

[0014] Preferably, the program-controlled AC power supply generates voltage pulses of corresponding amplitude and frequency under the control of preset amplitude and frequency parameters, and current excitation of the battery pack in a sweeping frequency manner through a DC blocking capacitor specifically includes:

[0015] Connect a DC blocking capacitor in series between the programmable AC power source and the battery pack to block the passage of DC current and only allow AC voltage pulses to provide current excitation to the battery pack;

[0016] Preset the start frequency, end frequency and step size of the sweep;

[0017] The programmable AC power supply will gradually change the frequency of the output voltage pulses according to the preset frequency parameters and step size.

[0018] Preferably, the host computer performs data error checking and data preprocessing on the received data specifically including:

[0019] At least one set of sample data is measured by experiment;

[0020] Verify the received data based on the preset value range of the battery data;

[0021] Determine whether the data is within the preset threshold range. If so, output the data correctly. If not, output the data incorrectly and delete the data.

[0022] Calculate the amplitude of the excitation current using the current formula;

[0023] The amplitude of the voltage response is calculated using the voltage formula;

[0024] Based on the amplitude of the excitation current and the amplitude of the voltage response, the internal resistance of each single cell is calculated using the battery internal resistance formula;

[0025] The current formula is:

[0026] ;

[0027] In the formula, To measure the function of the battery current changing with time, is the amplitude of the excitation current, is the battery output current, is the angular frequency of the excitation current, For time;

[0028] The voltage formula is:

[0029] ;

[0030] In the formula, To measure the voltage drop in the battery as a function of time, is the amplitude of the voltage response, is the battery output voltage, is the phase difference of the voltage pulse;

[0031] The battery internal resistance formula is:

[0032] ;

[0033] In the formula, is the internal resistance of each single cell.

[0034] Preferably, the characteristic parameters for real-time monitoring of the internal resistance of each single-chip battery specifically include:

[0035] Decompose the internal resistance of each single cell into real impedance and imaginary impedance in the complex plane;

[0036] The real part of the impedance represents the active resistance part inside the battery;

[0037] The imaginary impedance represents the passive resistance portion inside the battery, which is produced by the phase difference caused by the inductive and capacitive components of the battery;

[0038] Based on the real part of the impedance and the imaginary part of the impedance, the impedance amplitude modulus of the internal resistance of the battery is calculated using an impedance amplitude modulus formula;

[0039] The impedance amplitude modulus formula is:

[0040] ;

[0041] In the formula, is the impedance amplitude modulus of the battery internal resistance, is the real part of the battery internal resistance, is the imaginary part of the battery's internal resistance.

[0042] Preferably, the drawing and displaying of the electrochemical impedance spectrum of the internal resistance of each single-chip battery based on the characteristic parameters of the internal resistance of each single-chip battery specifically includes:

[0043] Based on the characteristic parameters of the internal resistance of each single-chip battery, the phase angle change of the impedance at each frequency is calculated using the phase angle formula;

[0044] The electrochemical impedance spectrum of each single cell internal resistance is plotted with the phase angle of impedance as the vertical axis and the frequency of the voltage pulse as the horizontal axis;

[0045] Determine whether the distance between each point and the adjacent point in the electrochemical impedance spectrum is higher than the preset threshold. If so, output the point as an abnormal point; if not, do not output it;

[0046] Eliminate abnormal points in the electrochemical impedance spectrum of each single cell internal resistance;

[0047] The phase angle formula is:

[0048] ;

[0049] In the formula, is the phase angle of impedance at each frequency.

[0050] Preferably, the curve fitting of the electrochemical impedance spectrum of the internal resistance of the single-chip battery specifically includes:

[0051] Construct an electrochemical impedance model of the internal resistance of a single cell;

[0052] Based on each measurement point in the electrochemical impedance spectrum of the internal resistance of the single-chip battery, the fitting points in the electrochemical impedance model are constructed;

[0053] Calculate the weighting coefficient of impedance data using the weighting coefficient formula;

[0054] Preset discriminant function based on weighting coefficients of impedance data;

[0055] Optimize the values ​​of each parameter in the electrochemical impedance model by using the value of the discriminant function;

[0056] Determine the best estimated values ​​of each parameter in the electrochemical impedance model so that the discriminant function takes the minimum value;

[0057] The weighting coefficient formula is:

[0058] ;

[0059] In the formula, is the weighting coefficient of the i-th measurement point, , are the real part and imaginary part of the impedance of the ith measurement point respectively;

[0060] The discriminant function is:

[0061] ;

[0062] In the formula, is the discriminant function value, is the total number of measurement points, , are the real and imaginary impedance parts of the i-th fitting point respectively.

[0063] Preferably, the model parameters of the equivalent circuit model of the battery pack are calculated specifically including:

[0064] Use the inductive reactance formula to calculate the inductive reactance of the battery pack;

[0065] Use the capacitive reactance formula to calculate the capacitive reactance of the battery pack;

[0066] Add the inductive reactance and capacitive reactance of the battery pack to obtain the ohmic impedance of the equivalent circuit model;

[0067] The polarization impedance of the equivalent circuit model is calculated using the polarization impedance formula;

[0068] The diffusion impedance of the equivalent circuit model is calculated using the diffusion impedance formula;

[0069] constructing an equivalent circuit model of the battery pack based on model parameters of the equivalent circuit model;

[0070] The inductive reactance formula is:

[0071] ;

[0072] In the formula, is the inductive reactance of the battery pack, is the output frequency of the battery pack, is the inductance of the battery pack;

[0073] The capacitive reactance formula is:

[0074] ;

[0075] In the formula, is the capacitive reactance of the battery pack, is the capacitance of the battery pack;

[0076] The polarization impedance formula is:

[0077] ;

[0078] In the formula, is the polarization impedance of the equivalent circuit model, is the corrosion current density, , are the Tafel slopes of the anodic and cathodic reactions, respectively;

[0079] The diffusion impedance formula is:

[0080] ;

[0081] In the formula, is the diffusion impedance of the equivalent circuit model, is the ideal gas constant, is the temperature, is the diffusion layer thickness, is the number of electrons, is the Faraday constant, is the effective reaction area, is the oxygen concentration in the cathode active layer, is the diffusion coefficient.

[0082] Preferably, the monitoring and diagnosis of the health status of the battery pack using the linear discriminant analysis method specifically includes:

[0083] Get the battery history fault type;

[0084] Obtain sample data of historical battery failures;

[0085] Establishing a linear discriminant function based on the sample data and the fault category;

[0086] Substituting the model parameters of the equivalent circuit model of the current battery pack into the linear discriminant function for calculation;

[0087] Determine whether the value of each linear discriminant function is greater than 0. If so, output the historical fault type of the battery as the current battery fault type. If not, no output is made.

[0088] The linear discriminant function is:

[0089] ;

[0090] In the formula, is the linear discriminant function of the ith fault type, is the first fault type in the i-th fault type The data feature weights, For the Data features, is the total number of data features.

[0091] Compared with the prior art, the present invention has the following beneficial effects:

[0092] It ensures that the battery pack receives stable and appropriate current excitation during the frequency sweep test, greatly improving the accuracy and reliability of the test. The application of DC blocking capacitors effectively isolates the DC component, further ensuring the purity of the test signal. The electrochemical impedance spectrum intuitively shows the law of battery internal resistance changing with frequency, providing strong visual support for the analysis and diagnosis of battery performance, and realizing comprehensive, accurate and real-time monitoring of the internal resistance state of the battery pack, providing strong technical support for the health management and performance optimization of the battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Figure 1 This is a flow chart of a method for monitoring the internal resistance of a battery based on a voltage pulse method according to the present invention;

[0094] Figure 2 This is a flow chart of a method for current excitation of a battery pack in a frequency sweeping manner according to the present invention;

[0095] Figure 3 It is a flow chart of the data error checking and data preprocessing method of the present invention;

[0096] Figure 4 This is a flow chart of a method for real-time monitoring of characteristic parameters of the internal resistance of each single-chip battery according to the present invention;

[0097] Figure 5 A flow chart of a method for drawing and displaying an electrochemical impedance spectroscopy diagram of the internal resistance of each single-chip battery according to the present invention;

[0098] Figure 6 A flow chart of a method for curve fitting of an electrochemical impedance spectrum of an internal resistance of a single-chip battery according to the present invention;

[0099] Figure 7 A flow chart of a method for calculating model parameters of an equivalent circuit model of a battery pack according to the present invention;

[0100] Figure 8 The present invention is a flow chart of a method for monitoring and diagnosing the health status of a battery pack using a linear discriminant analysis method. DETAILED DESCRIPTION

[0101] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art may think of other obvious variations.

[0102] Reference Figure 1 As shown, a battery internal resistance state monitoring method based on a voltage pulse method comprises:

[0103] Under the control of preset amplitude and frequency parameters, the programmable AC power supply generates voltage pulses of corresponding amplitude and frequency, and current excites the battery pack in a sweeping frequency manner through the DC isolation capacitor;

[0104] Complete the data collection of each single battery in the battery pack, and send the collected battery data to the host computer for data processing;

[0105] The host computer performs data error checking and data preprocessing on the received data;

[0106] Real-time monitoring of characteristic parameters of the internal resistance of each single-chip battery, wherein the characteristic parameters include impedance amplitude, impedance real part and impedance imaginary part;

[0107] Based on the characteristic parameters of the internal resistance of each single-chip battery, draw and display the electrochemical impedance spectrum of the internal resistance of each single-chip battery;

[0108] Perform curve fitting on the electrochemical impedance spectrum of the internal resistance of a single cell;

[0109] Calculating model parameters of an equivalent circuit model of a battery pack, wherein the model parameters include ohmic impedance, polarization impedance, and diffusion impedance;

[0110] Linear discriminant analysis is used to monitor and diagnose the health status of battery packs.

[0111] Battery internal resistance status monitoring usually uses constant current or constant voltage to charge or discharge the battery to obtain the battery performance parameters, and only performs simple data processing and status evaluation, and adopts rule-based or experience-based fault diagnosis methods. This paper generates voltage pulses through a programmable AC power supply with preset amplitude and frequency parameters, and excites the battery pack with current in a sweeping manner through a DC isolation capacitor. This method can more comprehensively understand the response characteristics of the battery at different frequencies, which is helpful for a deeper analysis of the battery performance. Based on the collected data, the electrochemical impedance spectrum of the internal resistance of each single-chip battery is drawn and displayed, and curve fitting is performed, which is helpful for a deeper understanding of the electrochemical process inside the battery, and the equivalent circuit model parameters of the battery pack are calculated, so as to more accurately evaluate the health status of the battery, and the linear discriminant analysis method is used to monitor and diagnose the health status of the battery pack. This method can more accurately identify possible problems in the battery pack and improve the accuracy and efficiency of diagnosis; the preset amplitude parameters can be adjusted according to actual needs, usually between 1V and 10V, and the preset frequency The sweep frequency range of the rate parameter is 1Hz to 1kHz, which covers the main frequency response area of ​​the electrochemical process inside the battery and helps to reveal the internal resistance, capacitance and other characteristics of the battery; a 1μF capacitor is selected to isolate the DC component to ensure the purity of the AC signal. In battery testing, the DC component may interfere with the test results, so a capacitor is needed to filter out these components; the sweep frequency is gradually increased from low frequency to high frequency, and the dwell time at each frequency point is set to 0.1 second. This time ensures that the battery has enough time to reach a stable state at this frequency, so as to obtain accurate test data; the data acquisition frequency is set to 100 times per second, and the data of each single-chip battery is collected independently. This frequency can ensure that the rapid changes in battery response are captured during the test; the spectrum range of the electrochemical impedance spectrum is consistent with the sweep frequency range, ensuring that the spectrum can cover all frequency responses during the test, and the spectrum resolution is set to one data point per 10Hz. This resolution can ensure that the electrochemical response characteristics of the battery at different frequencies are clearly displayed on the spectrum;

[0112] The usual internal resistance measurement method generally only measures voltage and current, and uses Ohm's law to obtain the internal resistance of the battery. However, this method involves very few physical quantities and has low fault tolerance. At the same time, according to common sense, internal resistance is easily affected by temperature. Therefore, when measuring, in order to ensure the accuracy of the data, multiple experiments must be carried out. That is, the battery will continue to operate, and the influence of its temperature will cause certain interference to the accuracy of the internal resistance measurement. In this scheme, a more complex mechanism is used for measurement. A large amount of data can be obtained through the short action of the voltage pulse. Since the voltage pulse has a short action time, it will not cause obvious changes in temperature. Therefore, during multiple measurements, the internal resistance can avoid the influence of temperature, and thus the measurement results are more in line with reality.

[0113] Reference Figure 2 As shown, under the control of preset amplitude and frequency parameters, the programmable AC power supply generates voltage pulses of corresponding amplitude and frequency, and current excitation of the battery pack is performed in a sweeping frequency manner through the DC isolation capacitor, specifically including:

[0114] Connect a DC blocking capacitor in series between the programmable AC power source and the battery pack to block the passage of DC current and only allow AC voltage pulses to provide current excitation to the battery pack;

[0115] Preset the start frequency, end frequency and step size of the sweep;

[0116] The programmable AC power supply will gradually change the frequency of the output voltage pulses according to the preset frequency parameters and step size.

[0117] Ensure that the programmable AC power supply, DC blocking capacitor, battery pack, and necessary test equipment and connecting wires are in good condition. Connect the DC blocking capacitor in series between the output end of the programmable AC power supply and the input end of the battery pack. The purpose of this is to utilize the characteristics of the DC blocking capacitor to prevent DC current from passing through, while allowing AC voltage pulses to be transmitted to the battery pack to achieve AC excitation of the battery pack. According to the test requirements, the required voltage pulse amplitude is preset through the control panel or software interface of the programmable AC power supply. The programmable DC power supply sets the output voltage and output current through external control, and sets the continuous current and voltage stability. The programmable DC power supply is controlled by a microcomputer, is stable, can be phase-shifted, and can provide sinusoidal signals at a constant current frequency.

[0118] Reference Figure 3 As shown, the host computer performs data error checking and data preprocessing on the received data, specifically including:

[0119] At least one set of sample data is measured by experiment;

[0120] Verify the received data based on the preset value range of the battery data;

[0121] Determine whether the data is within the preset threshold range. If so, output the data correctly. If not, output the data incorrectly and delete the data.

[0122] Calculate the amplitude of the excitation current using the current formula;

[0123] The amplitude of the voltage response is calculated using the voltage formula;

[0124] Based on the amplitude of the excitation current and the amplitude of the voltage response, the internal resistance of each single cell is calculated using the battery internal resistance formula;

[0125] The current formula is:

[0126] ;

[0127] In the formula, To measure the function of the battery current changing with time, is the amplitude of the excitation current, is the battery output current, is the angular frequency of the excitation current, For time;

[0128] The voltage formula is:

[0129] ;

[0130] In the formula, To measure the voltage drop in the battery as a function of time, is the amplitude of the voltage response, is the battery output voltage, is the phase difference of the voltage pulse;

[0131] The battery internal resistance formula is:

[0132] ;

[0133] In the formula, is the internal resistance of each single cell.

[0134] Here and can be fitted by experimental data, so by fitting the two groups and The measurement of can be based on the current formula, simultaneous equations, to obtain , and for the accuracy of the data, multiple The method of taking the average value is used to obtain a more accurate The value of can also be obtained through the voltage formula. , and then substitute the required quantity into the battery internal resistance formula to obtain the internal resistance of each single battery;

[0135] At least one set of sample data is measured from the battery system through experimental equipment or sensors to ensure that the experimental conditions are stable and the data acquisition equipment is accurately calibrated to ensure the reliability of the sample data. The host computer can perform effective error checking and preprocessing on the received battery data. The internal resistance of the battery refers to the resistance encountered by the current flowing through the battery when the battery is working. It includes ohmic internal resistance and polarization internal resistance. The polarization internal resistance includes electrochemical polarization internal resistance and concentration polarization internal resistance.

[0136] Reference Figure 4 As shown, the characteristic parameters for real-time monitoring of the internal resistance of each single-chip battery specifically include:

[0137] Decompose the internal resistance of each single cell into real impedance and imaginary impedance in the complex plane;

[0138] The real part of the impedance represents the active resistance part inside the battery;

[0139] The imaginary impedance represents the passive resistance portion inside the battery, which is produced by the phase difference caused by the inductive and capacitive components of the battery;

[0140] Based on the real part of the impedance and the imaginary part of the impedance, the impedance amplitude modulus of the internal resistance of the battery is calculated using an impedance amplitude modulus formula;

[0141] The impedance amplitude modulus formula is:

[0142] ;

[0143] In the formula, is the impedance amplitude modulus of the battery internal resistance, is the real part of the battery internal resistance, is the imaginary part of the battery's internal resistance.

[0144] There are two types of internal resistance in each single-chip battery, one is its own resistance, and the other is the impedance caused by the phase difference caused by the inductor and capacitor elements. The impedance will affect the internal resistance of the battery, which is also the normal situation of all batteries. Therefore, it is necessary to analyze this situation, otherwise, it is easy to cause misjudgment of the internal resistance monitoring situation, and the normal impedance situation will be warned as an abnormal situation. Therefore, the electrochemical impedance spectrum is subsequently constructed, and the curve is fitted based on this. Therefore, the computer can make its own judgment, and then this part can be taken into consideration during the monitoring process, which is more comprehensive than the usual use of current and voltage to measure resistance and conduct monitoring;

[0145] Equipped with a data acquisition system to record and store measurement results in real time, correctly connect the single-chip battery to be monitored to the measuring equipment to ensure good contact and avoid measurement errors. When performing impedance measurement, ensure that the battery is in a stable state to avoid the influence of external factors (such as temperature, vibration, etc.) on the measurement results. The impedance of the battery is a complex number, which represents the resistance of the battery to the AC signal. The amplitude, modulus, real part and imaginary part of the impedance jointly describe the impedance characteristics of the battery at different frequencies.

[0146] Reference Figure 5 As shown, based on the characteristic parameters of the internal resistance of each single-chip battery, drawing and displaying the electrochemical impedance spectrum of the internal resistance of each single-chip battery specifically includes:

[0147] Based on the characteristic parameters of the internal resistance of each single-chip battery, the phase angle change of the impedance at each frequency is calculated using the phase angle formula;

[0148] The electrochemical impedance spectrum of each single cell internal resistance is plotted with the phase angle of impedance as the vertical axis and the frequency of the voltage pulse as the horizontal axis;

[0149] Determine whether the distance between each point and the adjacent point in the electrochemical impedance spectrum is higher than the preset threshold. If so, output the point as an abnormal point; if not, do not output it;

[0150] Eliminate abnormal points in the electrochemical impedance spectrum of each single cell internal resistance;

[0151] The phase angle formula is:

[0152] ;

[0153] In the formula, is the phase angle of impedance at each frequency.

[0154] The internal resistance characteristic parameters of each single-chip battery under different conditions are collected to ensure that the data is accurate and has undergone necessary filtering or denoising processing to improve the accuracy of subsequent analysis. The phase angle change of impedance at each frequency is calculated using the phase angle formula. The purpose of this step is to convert the complex representation of impedance into a phase angle for intuitive display in the graph. The calculated phase angle at each frequency and the corresponding frequency value are marked in the coordinate system and connected into lines to form an electrochemical impedance spectrum of the internal resistance of each single-chip battery. The electrochemical impedance spectrum is an electrochemical characterization method that analyzes and studies the surface behavior of the target system such as the electrode kinetic process by measuring the change of the target system impedance with a given sinusoidal wave frequency. This technology is widely used in research fields such as corrosion and protection because it does not damage the target system such as the surface of the electrode to be tested.

[0155] Reference Figure 6 As shown, the curve fitting of the electrochemical impedance spectrum of the internal resistance of the single-chip battery specifically includes:

[0156] Construct an electrochemical impedance model of the internal resistance of a single cell;

[0157] Based on each measurement point in the electrochemical impedance spectrum of the internal resistance of the single-chip battery, the fitting points in the electrochemical impedance model are constructed;

[0158] Calculate the weighting coefficient of impedance data using the weighting coefficient formula;

[0159] Preset discriminant function based on weighting coefficients of impedance data;

[0160] Optimize the values ​​of each parameter in the electrochemical impedance model by using the value of the discriminant function;

[0161] Determine the best estimated values ​​of each parameter in the electrochemical impedance model so that the discriminant function takes the minimum value;

[0162] The weighting coefficient formula is:

[0163] ;

[0164] In the formula, is the weighting coefficient of the i-th measurement point, , are the real part and imaginary part of the impedance of the ith measurement point respectively;

[0165] The discriminant function is:

[0166] ;

[0167] In the formula, is the discriminant function value, is the total number of measurement points, , are the real and imaginary impedance parts of the i-th fitting point respectively.

[0168] According to the physical characteristics and electrochemical process of the battery, a suitable electrochemical impedance model is selected, and the values ​​of each component in the model are determined as the parameters to be fitted. The measured impedance spectrum data points are used as the fitting targets, that is, the model needs to be as close to these points as possible. The impedance spectrum predicted by the model is compared with the measured impedance spectrum, and the error or difference is calculated according to the discriminant function. The model parameters are iteratively adjusted to gradually reduce the value of the discriminant function until the preset convergence condition is reached. The measured impedance spectrum data is used to perform curve fitting and parameter estimation on the equivalent circuit model of the fuel cell, and important parameters of the fuel cell, such as ohmic impedance, polarization impedance, double-layer capacitance effect, and diffusion impedance, can be further obtained. Making full use of these parameters can comprehensively and accurately analyze the operating performance of the fuel cell, and can also be used to realize online health status monitoring and diagnosis of the fuel cell.

[0169] Reference Figure 7 As shown, the model parameters for calculating the equivalent circuit model of the battery pack specifically include:

[0170] Use the inductive reactance formula to calculate the inductive reactance of the battery pack;

[0171] Use the capacitive reactance formula to calculate the capacitive reactance of the battery pack;

[0172] Add the inductive reactance and capacitive reactance of the battery pack to obtain the ohmic impedance of the equivalent circuit model;

[0173] The polarization impedance of the equivalent circuit model is calculated using the polarization impedance formula;

[0174] The diffusion impedance of the equivalent circuit model is calculated using the diffusion impedance formula;

[0175] constructing an equivalent circuit model of the battery pack based on model parameters of the equivalent circuit model;

[0176] The inductive reactance formula is:

[0177] ;

[0178] In the formula, is the inductive reactance of the battery pack, is the output frequency of the battery pack, is the inductance of the battery pack;

[0179] The capacitive reactance formula is:

[0180] ;

[0181] In the formula, is the capacitive reactance of the battery pack, is the capacitance of the battery pack;

[0182] The polarization impedance formula is:

[0183] ;

[0184] In the formula, is the polarization impedance of the equivalent circuit model, is the corrosion current density, , are the Tafel slopes of the anodic and cathodic reactions, respectively;

[0185] The diffusion impedance formula is:

[0186] ;

[0187] In the formula, is the diffusion impedance of the equivalent circuit model, is the ideal gas constant, is the temperature, is the diffusion layer thickness, is the number of electrons, is the Faraday constant, is the effective reaction area, is the oxygen concentration in the cathode active layer, is the diffusion coefficient.

[0188] For battery packs, the inductance effects inside the battery and the connecting wires may need to be considered. If the inductance value in the battery pack is unknown, it can be estimated through experimental measurement or using empirical values. The capacitance effect in the battery pack may come from the double-layer capacitance inside the battery or the external parallel capacitance. Ohmic impedance is the resistance of the battery pack to DC current. Polarization impedance reflects the impedance generated by the battery during charging and discharging due to the electrode reaction kinetics and concentration polarization effects. Diffusion impedance is the impedance generated by the diffusion of ions inside the battery. It reflects the performance of the battery during high current charging and discharging. The constructed equivalent circuit model needs to be verified and adjusted through experimental data to ensure that it can accurately reflect the actual performance of the battery pack. This usually involves experimental measurements using methods such as electrochemical impedance spectroscopy and comparing the measurement results with model predictions.

[0189] Reference Figure 8 As shown, the use of linear discriminant analysis to monitor and diagnose the health status of the battery pack specifically includes:

[0190] Get the battery history fault type;

[0191] Obtain sample data of historical battery failures;

[0192] Establishing a linear discriminant function based on the sample data and the fault category;

[0193] Substituting the model parameters of the equivalent circuit model of the current battery pack into the linear discriminant function for calculation;

[0194] Determine whether the value of each linear discriminant function is greater than 0. If so, output the historical fault type of the battery as the current battery fault type. If not, no output is made.

[0195] The linear discriminant function is:

[0196] ;

[0197] In the formula, is the linear discriminant function of the ith fault type, is the first fault type in the i-th fault type The data feature weights, For the Data features, is the total number of data features.

[0198] Discriminant analysis is a statistical method that establishes discriminant functions and criteria based on known fault categories and their sample data, and then performs fault discrimination on unknown samples. Its characteristics are that all fault categories are clearly known in advance, and some sample data of each fault category are obtained through experiments and other methods. Through these sample data, the rules of system fault classification can be summarized, thereby establishing a fault discrimination model. When new samples appear, their fault types can be identified based on the discriminant model.

[0199] Furthermore, the present solution also proposes a computer-readable storage medium on which a computer-readable program is stored. When the computer-readable program is called, the above-mentioned battery internal resistance state monitoring method based on the voltage pulse method is executed.

[0200] It is understandable that the storage medium may be a magnetic medium, such as a floppy disk, a hard disk, or a magnetic tape; an optical medium, such as a DVD; or a semiconductor medium, such as a solid state drive (SSD).

[0201] In summary, the advantages of the present invention are: by online monitoring of important characteristic parameters of the battery, fuel cell health status monitoring and diagnosis can be achieved, and the specific reasons for the decline in fuel cell performance can be analyzed, and then by real-time adjustment and control of the corresponding working parameters of the fuel cell, system control can be optimized, performance loss can be reduced, and fuel cell performance can be improved, which is of great significance for ensuring the safe and efficient operation of the battery and extending its service life.

[0202] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A battery internal resistance state monitoring method based on a voltage pulse method, characterized in that: include: Under the control of preset amplitude and frequency parameters, the programmable AC power supply generates voltage pulses of corresponding amplitude and frequency, and current excites the battery pack in a sweeping frequency manner through the DC isolation capacitor; Complete the data collection of each single battery in the battery pack, and send the collected battery data to the host computer for data processing; The host computer performs data error checking and data preprocessing on the received data; Real-time monitoring of characteristic parameters of the internal resistance of each single-chip battery, wherein the characteristic parameters include impedance amplitude, impedance real part and impedance imaginary part; Based on the characteristic parameters of the internal resistance of each single-chip battery, draw and display the electrochemical impedance spectrum of the internal resistance of each single-chip battery; Perform curve fitting on the electrochemical impedance spectrum of the internal resistance of a single cell; Calculating model parameters of an equivalent circuit model of a battery pack, wherein the model parameters include ohmic impedance, polarization impedance, and diffusion impedance; Linear discriminant analysis is used to monitor and diagnose the health status of battery packs.

2. A battery internal resistance state monitoring method based on voltage pulse method according to claim 1, characterized in that: The program-controlled AC power supply generates voltage pulses of corresponding amplitude and frequency under the control of preset amplitude and frequency parameters, and current excitation is performed on the battery pack in a frequency sweeping manner through a DC isolation capacitor, specifically including: Connect a DC blocking capacitor in series between the programmable AC power source and the battery pack to block the passage of DC current and only allow AC voltage pulses to provide current excitation to the battery pack; Preset the start frequency, end frequency and step size of the sweep; The programmable AC power supply will gradually change the frequency of the output voltage pulses according to the preset frequency parameters and step size.

3. The method for monitoring the internal resistance of a battery based on a voltage pulse method according to claim 2, characterized in that: The host computer performs data error checking and data preprocessing on the received data, specifically including: At least one set of sample data is measured by experiment; Verify the received data based on the preset value range of the battery data; Determine whether the data is within the preset threshold range. If so, output the data correctly. If not, output the data incorrectly and delete the data. Calculate the amplitude of the excitation current using the current formula; The amplitude of the voltage response is calculated using the voltage formula; Based on the amplitude of the excitation current and the amplitude of the voltage response, the internal resistance of each single cell is calculated using the battery internal resistance formula; The current formula is: ； In the formula, To measure the function of the battery current changing with time, is the amplitude of the excitation current, is the battery output current, is the angular frequency of the excitation current, For time; The voltage formula is: ； In the formula, To measure the voltage drop in the battery as a function of time, is the amplitude of the voltage response, is the battery output voltage, is the phase difference of the voltage pulse; The battery internal resistance formula is: ； In the formula, is the internal resistance of each single cell.

4. The method for monitoring the internal resistance of a battery based on a voltage pulse method according to claim 3, characterized in that: The characteristic parameters for real-time monitoring of the internal resistance of each single-chip battery specifically include: Decompose the internal resistance of each single cell into real impedance and imaginary impedance in the complex plane; The real part of the impedance represents the active resistance part inside the battery; The imaginary impedance represents the passive resistance portion inside the battery, which is produced by the phase difference caused by the inductive and capacitive components of the battery; Based on the real part of the impedance and the imaginary part of the impedance, the impedance amplitude modulus of the internal resistance of the battery is calculated using an impedance amplitude modulus formula; The impedance amplitude modulus formula is: ； In the formula, is the impedance amplitude modulus of the battery internal resistance, is the real part of the battery internal resistance, is the imaginary part of the battery's internal resistance.

5. The method for monitoring the internal resistance of a battery based on a voltage pulse method according to claim 4, characterized in that: Drawing and displaying the electrochemical impedance spectrum of the internal resistance of each single-chip battery based on the characteristic parameters of the internal resistance of each single-chip battery specifically includes: Based on the characteristic parameters of the internal resistance of each single-chip battery, the phase angle change of the impedance at each frequency is calculated using the phase angle formula; The electrochemical impedance spectrum of each single cell internal resistance is plotted with the phase angle of impedance as the vertical axis and the frequency of the voltage pulse as the horizontal axis; Determine whether the distance between each point and the adjacent point in the electrochemical impedance spectrum is higher than the preset threshold. If so, output the point as an abnormal point; if not, do not output it; Eliminate abnormal points in the electrochemical impedance spectrum of each single cell internal resistance; The phase angle formula is: ； In the formula, is the phase angle of impedance at each frequency.

6. A battery internal resistance state monitoring method based on voltage pulse method according to claim 5, characterized in that: The curve fitting of the electrochemical impedance spectrum of the internal resistance of the single-chip battery specifically includes: Construct an electrochemical impedance model of the internal resistance of a single cell; Based on each measurement point in the electrochemical impedance spectrum of the internal resistance of the single-chip battery, the fitting points in the electrochemical impedance model are constructed; Calculate the weighting coefficient of impedance data using the weighting coefficient formula; Preset discriminant function based on weighting coefficients of impedance data; Optimize the values ​​of each parameter in the electrochemical impedance model by using the value of the discriminant function; Determine the best estimated values ​​of each parameter in the electrochemical impedance model so that the discriminant function takes the minimum value; The weighting coefficient formula is: ； In the formula, is the weighting coefficient of the i-th measurement point, , are the real part and imaginary part of the impedance of the ith measurement point respectively; The discriminant function is: ； In the formula, is the discriminant function value, is the total number of measurement points, , are the real and imaginary impedance parts of the i-th fitting point respectively.

7. A battery internal resistance state monitoring method based on voltage pulse method according to claim 6, characterized in that: The model parameters of the equivalent circuit model of the battery pack are calculated specifically including: Use the inductive reactance formula to calculate the inductive reactance of the battery pack; Use the capacitive reactance formula to calculate the capacitive reactance of the battery pack; Add the inductive reactance and capacitive reactance of the battery pack to obtain the ohmic impedance of the equivalent circuit model; The polarization impedance of the equivalent circuit model is calculated using the polarization impedance formula; The diffusion impedance of the equivalent circuit model is calculated using the diffusion impedance formula; constructing an equivalent circuit model of the battery pack based on model parameters of the equivalent circuit model; The inductive reactance formula is: ； In the formula, is the inductive reactance of the battery pack, is the output frequency of the battery pack, is the inductance of the battery pack; The capacitive reactance formula is: ； In the formula, is the capacitive reactance of the battery pack, is the capacitance of the battery pack; The polarization impedance formula is: ； In the formula, is the polarization impedance of the equivalent circuit model, is the corrosion current density, , are the Tafel slopes of the anodic and cathodic reactions, respectively; The diffusion impedance formula is: ； In the formula, is the diffusion impedance of the equivalent circuit model, is the ideal gas constant, is the temperature, is the diffusion layer thickness, is the number of electrons, is the Faraday constant, is the effective reaction area, is the oxygen concentration in the cathode active layer, is the diffusion coefficient.

8. The method for monitoring the internal resistance of a battery based on a voltage pulse method according to claim 7, characterized in that: The monitoring and diagnosis of the health status of the battery pack using the linear discriminant analysis method specifically includes: Get the battery history fault type; Obtain sample data of historical battery failures; Establishing a linear discriminant function based on the sample data and the fault category; Substituting the model parameters of the equivalent circuit model of the current battery pack into the linear discriminant function for calculation; Determine whether the value of each linear discriminant function is greater than 0. If so, output the historical fault type of the battery as the current battery fault type. If not, no output is made. The linear discriminant function is: ； In the formula, is the linear discriminant function of the ith fault type, is the first fault type in the i-th fault type The data feature weights, For the Data features, is the total number of data features.

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