Capacitor health state assessment method, device and equipment based on multi-frequency impedance curve inflection point change

Abstract

The invention relates to a capacitor health state assessment method, device and equipment based on multi-frequency impedance curve inflection point change. The method comprises the steps that fast Fourier transform is carried out on a to-be-assessed capacitor reference and all actually measured time-domain currents and time-domain voltages to obtain frequency-domain currents and frequency-domain voltages; according to the frequency domain current, the frequency domain voltage, each sampling resolution and the capacitance value, calculating to obtain total impedance, a capacitive reactance value and equivalent series resistance; constructing a reference impedance curve and a real-time impedance curve according to each sampling resolution and the corresponding equivalent series resistance in the reference data and the actually measured real-time data; respectively processing the reference impedance curve and the real-time impedance curve to obtain an inflection point offset and a slope offset total value; acquiring an inflection point offset set value and a slope offset set value, and calculating health state index data according to the inflection point offset, the inflection point offset set value, the slope offset total value and the slope offset set value; and judging the health degree of the to-be-evaluated capacitor according to the health state index data.

Description

Technical Field

[0001] The present application relates to the technical field of capacitors, and in particular to a method, apparatus, and device for evaluating the health status of a capacitor based on changes in the inflection points of a multi-frequency impedance curve. Background Art

[0002] Metallized film capacitors, thanks to their exceptional self-healing capabilities, high energy density, and excellent electrical properties, have been widely used in a variety of applications, including high-voltage direct current (HVDC) transmission systems, modular multilevel converters (MMCs), and renewable energy generation. However, over long-term operation, capacitors can gradually experience performance degradation due to multiple factors, including dielectric material aging, electrode degradation, self-healing effects, and environmental conditions. In severe cases, these degradations can lead to failure. Therefore, effective capacitor status monitoring to assess aging and failure risk is crucial.

[0003] In modular multilevel converters (MMCs), there are a large number of metallized film capacitors, often reaching hundreds or even thousands. Due to their packaging, they are difficult to disassemble, and testing each capacitor individually consumes a significant amount of manpower and material resources. Most existing health monitoring technologies for metallized film capacitors only support offline testing or require equipment shutdown, failing to meet real-time monitoring requirements. Furthermore, existing technologies primarily rely on single characteristic quantities, such as capacitance and dielectric loss tangent, for judgment. However, these parameters reflect different failure modes at different frequencies, making it difficult to comprehensively assess the various degradation states of the capacitors. Furthermore, the analytical accuracy of existing health monitoring technologies for metallized film capacitors is significantly insufficient when faced with complex dynamic operating conditions, such as those of the submodules of modular multilevel converters (MMCs). These technical bottlenecks severely restrict the reliability of condition monitoring and the accuracy of life prediction for metallized film capacitors in highly dynamic application scenarios. Summary of the Invention

[0004] The present application provides a capacitor health status assessment method, device and equipment based on the inflection point changes of a multi-frequency impedance curve, which is used to solve the technical problem that the existing metallized film capacitor health status monitoring technology has low accuracy, which seriously restricts the reliability of status monitoring and the accuracy of life prediction of metallized film capacitors in high dynamic application scenarios.

[0005] In order to achieve the above objectives, this application provides the following technical solutions:

[0006] In one aspect, a method for evaluating the health status of a capacitor based on the inflection point change of a multi-frequency impedance curve is provided, comprising the following steps:

[0007] Obtaining baseline data and measured real-time data of the capacitor to be evaluated, wherein the baseline data and the measured real-time data both include the capacitance value of the capacitor to be evaluated, various sampling resolutions, and time-domain current and time-domain voltage of the capacitor to be evaluated obtained according to all the sampling resolutions;

[0008] Processing all the time-domain currents and all the time-domain voltages respectively using fast Fourier transform to obtain a frequency-domain current corresponding to each time-domain current and a frequency-domain voltage corresponding to each time-domain voltage;

[0009] Calculating based on the frequency domain current and the frequency domain voltage of each sampling resolution to obtain a total impedance corresponding to the sampling resolution; calculating based on each sampling resolution and the capacitance value to obtain a capacitive reactance value corresponding to the sampling resolution; calculating based on the capacitive reactance value of each sampling resolution and the total impedance to obtain an equivalent series resistance corresponding to the sampling resolution;

[0010] Constructing a reference impedance curve based on each sampling resolution and the corresponding equivalent series resistance in the reference data; constructing a real-time impedance curve based on each sampling resolution and the corresponding equivalent series resistance in the measured real-time data;

[0011] The reference impedance curve and the real-time impedance curve are processed separately to obtain reference inflection point data and a reference slope curve corresponding to the reference impedance curve, and real-time impedance inflection point data and a real-time impedance slope curve corresponding to the real-time impedance curve; an inflection point offset is obtained by calculation based on the reference inflection point data and the real-time impedance inflection point data; and a total slope offset is obtained by calculation based on the data in the reference slope curve and the real-time impedance slope curve;

[0012] Obtaining an inflection point offset set value and a slope offset set value, calculating an inflection point change based on the inflection point offset and the inflection point offset set value; calculating a slope offset change based on the slope offset total value and the slope offset set value; performing a weighted calculation based on the inflection point change and the slope offset change to obtain health status indicator data of the capacitor to be evaluated;

[0013] The health status of the capacitor to be evaluated is determined according to the health status indicator data.

[0014] Preferably, the equivalent series resistance corresponding to the sampling resolution is obtained based on the capacitive reactance value and the total impedance of each sampling resolution, including: subtracting the square of the capacitive reactance value corresponding to the sampling resolution from the square of the total impedance of each sampling resolution to obtain the impedance difference of the sampling resolution; and then taking the square root of the impedance difference to obtain the equivalent series resistance corresponding to the sampling resolution.

[0015] Preferably, processing the reference impedance curve and the real-time impedance curve separately to obtain reference inflection point data and a reference slope curve corresponding to the reference impedance curve and real-time impedance inflection point data and a real-time impedance slope curve corresponding to the real-time impedance curve includes:

[0016] Determine a reference impedance function according to the reference impedance curve, and determine a real-time impedance function according to the real-time impedance curve;

[0017] Solving the second-order derivative of the reference impedance function to obtain reference inflection point data; solving the second-order derivative of the real-time impedance function to obtain real-time impedance inflection point data;

[0018] Obtaining the parallel resistance value of the capacitor to be evaluated and the series capacitance value of the series resistor, and calculating based on the parallel resistance value, the series capacitance value, and two adjacent sampling resolutions in the reference impedance curve to obtain a reference curve slope between the two adjacent sampling resolutions; and calculating based on the parallel resistance value, the series capacitance value, and two adjacent sampling resolutions in the real-time impedance curve to obtain a real-time curve slope between the two adjacent sampling resolutions;

[0019] A reference slope curve is constructed based on all the reference curve slopes with frequency as the horizontal coordinate and curve slope as the vertical coordinate; a real-time impedance slope curve is constructed based on all the real-time curve slopes with frequency as the horizontal coordinate and curve slope as the vertical coordinate.

[0020] Preferably, the total slope offset value is obtained by calculating based on the data in the reference slope curve and the real-time impedance slope curve, including: performing difference calculation on the real-time curve slope of each frequency in the real-time impedance slope curve and the reference curve slope of the corresponding frequency in the reference slope curve to obtain the slope offset of each frequency; and integrating all the slope offsets to obtain the total slope offset value.

[0021] Preferably, the inflection point offset is obtained by calculating based on the benchmark inflection point data and the real-time impedance inflection point data, including: subtracting the benchmark inflection point data from the real-time impedance inflection point data to obtain the inflection point offset difference; and dividing the inflection point offset difference by the benchmark inflection point data to obtain the inflection point offset.

[0022] Preferably, the capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve includes: dividing the inflection point offset by the inflection point offset setting value to obtain the inflection point offset rate, and subtracting the inflection point offset rate from 1 to obtain the inflection point change; dividing the total slope offset value by the slope offset setting value to obtain the slope curve rate, and subtracting the slope curve rate from 1 to obtain the slope offset change; multiplying the inflection point change by a first weight coefficient to obtain first indicator data, multiplying the slope offset change by a second weight coefficient to obtain second indicator data, and adding the first indicator data to the second indicator data to obtain the health status indicator data of the capacitor to be evaluated.

[0023] Preferably, judging the health of the capacitor to be evaluated according to the health status indicator data includes:

[0024] If the health status indicator data is less than the first set value and greater than 0, the health status of the capacitor to be evaluated is in a severely degraded state;

[0025] If the health status indicator data is not less than the first set value and less than the second set value, the health status of the capacitor to be evaluated is in a moderately degraded state;

[0026] If the health status indicator data is not less than the second set value and less than the third set value, the health status of the capacitor to be evaluated is in a slightly degraded state;

[0027] If the health status indicator data is not less than the third set value and less than the fourth set value, the health status of the capacitor to be evaluated is in a healthy state.

[0028] On the other hand, a capacitor health status assessment device based on the inflection point change of a multi-frequency impedance curve is provided, comprising a data acquisition module, a data processing module, a first calculation module, a curve construction module, a second calculation module, a third calculation module and a judgment module;

[0029] The data acquisition module is configured to acquire baseline data and measured real-time data of the capacitor to be evaluated, wherein the baseline data and the measured real-time data each include the capacitance value of the capacitor to be evaluated, various sampling resolutions, and time-domain current and time-domain voltage of the capacitor to be evaluated obtained according to all the sampling resolutions;

[0030] The data processing module is configured to process all the time-domain currents and all the time-domain voltages using fast Fourier transform to obtain a frequency-domain current corresponding to each time-domain current and a frequency-domain voltage corresponding to each time-domain voltage;

[0031] The first calculation module is configured to calculate, based on the frequency domain current and the frequency domain voltage of each sampling resolution, a total impedance corresponding to the sampling resolution; calculate, based on each sampling resolution and the capacitance value, a capacitive reactance value corresponding to the sampling resolution; and calculate, based on the capacitive reactance value of each sampling resolution and the total impedance, an equivalent series resistance corresponding to the sampling resolution;

[0032] The curve construction module is used to construct a reference impedance curve according to each sampling resolution and the corresponding equivalent series resistance in the reference data; and to construct a real-time impedance curve according to each sampling resolution and the corresponding equivalent series resistance in the measured real-time data;

[0033] The second calculation module is used to process the reference impedance curve and the real-time impedance curve respectively to obtain reference inflection point data and a reference slope curve corresponding to the reference impedance curve, and real-time impedance inflection point data and a real-time impedance slope curve corresponding to the real-time impedance curve; calculate based on the reference inflection point data and the real-time impedance inflection point data to obtain an inflection point offset; calculate based on the data in the reference slope curve and the real-time impedance slope curve to obtain a total slope offset;

[0034] The third calculation module is configured to obtain an inflection point offset setting value and a slope offset setting value, calculate an inflection point variation based on the inflection point offset and the inflection point offset setting value; calculate a slope offset variation based on the slope offset total value and the slope offset setting value; and perform a weighted calculation based on the inflection point variation and the slope offset variation to obtain health status indicator data of the capacitor to be evaluated;

[0035] The judgment module is used to judge the health status of the capacitor to be evaluated according to the health status indicator data.

[0036] Preferably, the third calculation module is further used to divide the inflection point offset by the inflection point offset setting value to obtain the inflection point offset rate, and subtract the inflection point offset rate from 1 to obtain the inflection point change; divide the total slope offset value by the slope offset setting value to obtain the slope curve rate, and subtract the slope curve rate from 1 to obtain the slope offset change; multiply the inflection point change by a first weight coefficient to obtain first indicator data, multiply the slope offset change by a second weight coefficient to obtain second indicator data, and add the first indicator data and the second indicator data to obtain the health status indicator data of the capacitor to be evaluated.

[0037] In another aspect, a terminal device is provided, comprising a processor and a memory;

[0038] The memory is used to store program code and transmit the program code to the processor;

[0039] The processor is configured to execute the above-mentioned capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve according to the instructions in the program code.

[0040] The capacitor health status assessment method, device and equipment based on the inflection point change of the multi-frequency impedance curve include obtaining the baseline data and measured real-time data of the capacitor to be evaluated, wherein the baseline data and the measured real-time data both include the capacitance value of the capacitor to be evaluated, each sampling resolution, and obtaining the time domain current and time domain voltage of the capacitor to be evaluated according to all sampling resolutions; all time domain currents and all time domain voltages are processed by fast Fourier transform respectively to obtain the frequency domain current corresponding to each time domain current and the frequency domain voltage corresponding to each time domain voltage; the total impedance corresponding to the sampling resolution is obtained based on the frequency domain current and frequency domain voltage of each sampling resolution; the capacitive reactance value corresponding to the sampling resolution is calculated based on each sampling resolution and the capacitance value; the equivalent series resistance corresponding to the sampling resolution is calculated based on the capacitive reactance value and the total impedance of each sampling resolution; the equivalent series resistance corresponding to the sampling resolution is obtained based on the capacitance .... and the corresponding equivalent series resistance to construct a benchmark impedance curve; construct a real-time impedance curve according to each sampling resolution and the corresponding equivalent series resistance in the measured real-time data; process the benchmark impedance curve and the real-time impedance curve respectively to obtain benchmark inflection point data and a benchmark slope curve corresponding to the benchmark impedance curve, and real-time impedance inflection point data and a real-time impedance slope curve corresponding to the real-time impedance curve; calculate based on the benchmark inflection point data and the real-time impedance inflection point data to obtain an inflection point offset; calculate based on the data in the benchmark slope curve and the real-time impedance slope curve to obtain a total slope offset; obtain an inflection point offset setting value and a slope offset setting value, and calculate based on the inflection point offset and the inflection point offset setting value to obtain an inflection point change; calculate based on the total slope offset value and the slope offset setting value to obtain a slope offset change; perform weighted calculation based on the inflection point change and the slope offset change to obtain health status index data of the capacitor to be evaluated; and judge the health status index data of the capacitor to be evaluated.

[0041] It can be seen from the above technical solutions that the present application has the following advantages: the capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve collects the baseline data and measured real-time data of the capacitor to be evaluated and calculates the corresponding equivalent series resistance based on its current data and voltage data. Then, different frequencies are substituted one by one to obtain the impedance curve of the equivalent series resistance with respect to the sampling resolution; during the degradation process of the capacitor, the impedance curve will change, which is specifically reflected in the inflection point and slope of the curve; then, by comparing the baseline impedance curve of the capacitor in a healthy state, the degree of degradation of the capacitor to be evaluated can be determined, and online health status monitoring and accurate assessment of the capacitor under the operating conditions of power equipment can be realized, which solves the low accuracy of the existing health status monitoring technology of metallized film capacitors, which seriously restricts the reliability of status monitoring and life prediction accuracy of metallized film capacitors in high dynamic application scenarios.

[0042] This capacitor health status assessment device based on the inflection point change of the multi-frequency impedance curve realizes the health status assessment of the capacitor under operation state through the real-time dynamic monitoring technology of the capacitor to be evaluated through the data acquisition module, data processing module, first calculation module, curve construction module, second calculation module, third calculation module and judgment module, without stopping the machine for detection. The baseline data and measured real-time data of the capacitor to be evaluated are collected and the corresponding equivalent series resistance is calculated based on its current data and voltage data. Then, different frequencies are substituted one by one to obtain the impedance curve of the equivalent series resistance with respect to the sampling resolution; during the degradation process of the capacitor, the impedance curve will change, which is specifically reflected in the inflection point of the curve and the slope of the curve; then, by comparing the baseline impedance curve of the capacitor in the healthy state, the degree of degradation of the capacitor to be evaluated can be judged, realizing the online health status monitoring and accurate assessment of the capacitor under the operating conditions of the power equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0044] Figure 1 This is a flowchart of the steps of the capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve according to an embodiment of the present application;

[0045] Figure 2 This is a schematic diagram of the framework of the capacitor health status assessment device based on the inflection point change of the multi-frequency impedance curve according to an embodiment of the present application;

[0046] Figure 3This is a schematic diagram of the terminal device described in an embodiment of the present application. DETAILED DESCRIPTION

[0047] In order to make the purpose, features, and advantages of the invention of this application more obvious and easy to understand, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the embodiments described below are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0048] In the description of the embodiments of the present application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0049] In the embodiments of the present application, unless otherwise expressly specified or limited, the terms "installed," "connected," "connected," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections, electrical connections; direct connections, or indirect connections through an intermediate medium; internal connections between two components, or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0050] In this patent application:

[0051] The Fast Fourier Transform (FFT) is an efficient algorithm for the Discrete Fourier Transform (DFT). The Fourier transform is one of the most fundamental methods in time-domain to frequency-domain analysis. The Fourier transform recursively decomposes the Discrete Fourier Transform (DFT) into shorter DFTs, allowing for faster implementation of the original function.

[0052] The embodiments of the present application provide a method, device and equipment for evaluating the health status of a capacitor based on the inflection point changes of a multi-frequency impedance curve, which solves the technical problem that the existing technology for monitoring the health status of metallized film capacitors has low accuracy, which seriously restricts the reliability of status monitoring and the accuracy of life prediction of metallized film capacitors in high-dynamic application scenarios.

[0053] Example 1:

[0054] Figure 1This is a flowchart of the steps of the capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve described in an embodiment of the present application.

[0055] like Figure 1 As shown, the embodiment of the present application provides a capacitor health status assessment method based on the inflection point change of a multi-frequency impedance curve, comprising the following steps:

[0056] S1. Obtain baseline data and measured real-time data of the capacitor to be evaluated. The baseline data and measured real-time data both include the capacitance value of the capacitor to be evaluated, various sampling resolutions, and time-domain current and time-domain voltage of the capacitor to be evaluated obtained based on all sampling resolutions.

[0057] It should be noted that in step S1, baseline data of the capacitor to be evaluated in its initial healthy state and measured real-time data of the capacitor to be evaluated after a period of use are obtained, providing data for the subsequent steps of analyzing the capacitor to be evaluated. In this embodiment, the measured real-time data of the capacitor to be evaluated after a period of use is obtained based on a sampling resolution of 50 Hz and a sampling frequency range of 0 Hz to 20 kHz to obtain 4000 time-domain currents and 4000 time-domain voltages, ensuring sufficient sampling of high-frequency signals in the capacitor to be evaluated. The baseline data of the capacitor to be evaluated in its initial healthy state is obtained based on a sampling resolution of 50 Hz and a sampling frequency range of 0 Hz to 20 kHz to obtain 4000 time-domain currents and 4000 time-domain voltages.

[0058] In an embodiment of the present application, in the process of obtaining the baseline data and the measured real-time data of the capacitor to be evaluated, the time domain voltage and time domain current of the baseline data or the measured real-time data of the capacitor to be evaluated are collected by a data acquisition device (such as a Hall effect current sensor and a high-precision voltage sensor).

[0059] It should be noted that during time-domain voltage acquisition, the power supply is connected to the capacitor under evaluation through a protective resistor, and a high-precision voltage sensor is connected across the capacitor under evaluation. During time-domain current acquisition, a Hall-effect current sensor is installed in the current loop through the capacitor under evaluation, enabling real-time acquisition of the current signal flowing through the capacitor under evaluation.

[0060] S2. All time-domain currents and all time-domain voltages are processed using fast Fourier transform to obtain a frequency-domain current corresponding to each time-domain current and a frequency-domain voltage corresponding to each time-domain voltage.

[0061] It should be noted that in step S2, a fast Fourier transform is performed on each time-domain current and time-domain voltage of the baseline data and the measured real-time data obtained in step S1 to obtain a frequency-domain current corresponding to each time-domain current and a frequency-domain voltage corresponding to each time-domain voltage, providing data for the subsequent steps of calculating the total impedance, capacitive reactance, and equivalent series resistance. In this embodiment, if the time-domain current is denoted as I(t) and the time-domain voltage is denoted as V(t), the time-domain current I(t) is converted to the frequency-domain current I(f) by a fast Fourier transform, and the time-domain voltage V(t) is converted to the frequency-domain voltage V(f) by a fast Fourier transform.

[0062] In an embodiment of the present application, all time-domain currents and all time-domain voltages are processed by fast Fourier transform respectively to obtain the frequency-domain current corresponding to each time-domain current and the frequency-domain voltage corresponding to each time-domain voltage. The capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve includes: removing low-frequency drift from all time-domain currents and all time-domain voltages through a filter, and normalizing each time-domain current and time-domain voltage to eliminate amplitude dimension differences and improve the accuracy of the provided data.

[0063] S3. Calculate the total impedance corresponding to each sampling resolution based on the frequency domain current and frequency domain voltage; calculate the capacitive reactance value corresponding to each sampling resolution based on the capacitance value; and calculate the equivalent series resistance corresponding to each sampling resolution based on the capacitive reactance value and the total impedance.

[0064] It should be noted that in step S3, the total impedance, capacitive impedance, and equivalent series resistance of each sampling resolution are calculated based on the data obtained in step S2, providing data for constructing the impedance curve in the subsequent steps. In this embodiment, the total impedance formula is used to calculate the total impedance corresponding to the sampling resolution based on the frequency domain current and frequency domain voltage of each sampling resolution. The capacitive reactance formula is used to calculate the capacitive reactance value corresponding to the sampling resolution based on each sampling resolution and capacitance value.

[0065] In the embodiment of the present application, the total impedance formula is: Z(f)=V(f) / I(f); the capacitive reactance formula is: X(f)=1 / (2πfC), where Z(f) is the total impedance with a sampling resolution of f, V(f) is the frequency domain voltage with a sampling resolution of f, I(f) is the frequency domain current with a sampling resolution of f, X(f) is the capacitive reactance value with a sampling resolution of f, f is the sampling resolution, and C is the capacitance value of the capacitor to be evaluated.

[0066] S4. Construct a reference impedance curve based on each sampling resolution and the corresponding equivalent series resistance in the reference data; construct a real-time impedance curve based on each sampling resolution and the corresponding equivalent series resistance in the measured real-time data.

[0067] It should be noted that in step S4, the various sampling resolutions and the equivalent series resistance corresponding to the various sampling resolutions are obtained according to step S3, and the reference impedance curve and the real-time impedance curve are constructed with the sampling resolution as the horizontal coordinate and the equivalent series resistance as the vertical coordinate, so as to provide data for obtaining the reference inflection point data, the reference slope curve, the real-time impedance inflection point data and the real-time impedance slope curve in the subsequent steps.

[0068] S5. Process the baseline impedance curve and the real-time impedance curve separately to obtain the baseline inflection point data and the baseline slope curve corresponding to the baseline impedance curve, and the real-time impedance inflection point data and the real-time impedance slope curve corresponding to the real-time impedance curve; calculate based on the baseline inflection point data and the real-time impedance inflection point data to obtain the inflection point offset; calculate based on the data in the baseline slope curve and the real-time impedance slope curve to obtain the total slope offset value.

[0069] It should be noted that in step S5, the baseline impedance curve and the real-time impedance curve obtained in step S4 are processed to first obtain the baseline inflection point data, the baseline slope curve, the real-time impedance inflection point data and the real-time impedance slope curve. Then, the inflection point offset is calculated based on the baseline inflection point data and the real-time impedance inflection point data, and the total slope offset is calculated based on the data in the baseline slope curve and the real-time impedance slope curve to provide data for the subsequent steps of calculating the health status indicator data.

[0070] S6. Obtain the inflection point offset setting value and the slope offset setting value, calculate the inflection point change based on the inflection point offset and the inflection point offset setting value; calculate the slope offset change based on the total slope offset value and the slope offset setting value; perform weighted calculation based on the inflection point change and the slope offset change to obtain the health status indicator data of the capacitor to be evaluated.

[0071] It should be noted that in step S6, the inflection point offset setting value and the slope offset setting value are first obtained, and then the inflection point offset setting value and the slope offset setting value are calculated based on the inflection point offset, the total slope offset value, and the obtained inflection point offset setting value and the slope offset setting value, to provide data for subsequent evaluation of the health of the capacitor to be evaluated.

[0072] S7. Determine the health status of the capacitor to be evaluated based on the health status indicator data.

[0073] It should be noted that step S7 analyzes the health of the capacitor to be evaluated after a period of use based on the health indicator data obtained in step S6. In this embodiment, this capacitor health assessment method based on inflection point changes in a multi-frequency impedance curve utilizes real-time dynamic monitoring technology to assess the health of the capacitor under operation without requiring downtime for testing.

[0074] The present application provides a capacitor health status assessment method based on the inflection point change of a multi-frequency impedance curve, which includes obtaining baseline data and measured real-time data of the capacitor to be evaluated, wherein both the baseline data and the measured real-time data include the capacitance value of the capacitor to be evaluated, each sampling resolution, and obtaining the time domain current and time domain voltage of the capacitor to be evaluated according to all sampling resolutions; all time domain currents and all time domain voltages are processed by fast Fourier transform respectively to obtain the frequency domain current corresponding to each time domain current and the frequency domain voltage corresponding to each time domain voltage; the total impedance corresponding to the sampling resolution is obtained by calculating the frequency domain current and frequency domain voltage of each sampling resolution; the capacitive reactance value corresponding to the sampling resolution is obtained by calculating the capacitive reactance value corresponding to the sampling resolution according to each sampling resolution and the capacitance value; the equivalent series resistance corresponding to the sampling resolution is obtained by calculating the capacitive reactance value and the total impedance of each sampling resolution; and the equivalent series resistance corresponding to the sampling resolution is constructed according to each sampling resolution and the corresponding equivalent series resistance in the baseline data. A baseline impedance curve is constructed based on the sampling resolutions and corresponding equivalent series resistances in the measured real-time data. The baseline impedance curve and the real-time impedance curve are processed separately to obtain baseline inflection point data and a baseline slope curve corresponding to the baseline impedance curve, as well as real-time impedance inflection point data and a real-time impedance slope curve corresponding to the real-time impedance curve. An inflection point offset is calculated based on the baseline inflection point data and the real-time impedance inflection point data. A total slope offset value is calculated based on the data in the baseline slope curve and the real-time impedance slope curve. An inflection point offset setting value and a slope offset setting value are obtained, and an inflection point change is calculated based on the inflection point offset and the inflection point offset setting value. A slope offset change is calculated based on the total slope offset value and the slope offset setting value. A weighted calculation is performed based on the inflection point change and the slope offset change to obtain health status index data of the capacitor to be evaluated. The health status of the capacitor to be evaluated is determined based on the health status index data. This capacitor health status assessment method based on inflection point change of a multi-frequency impedance curve collects baseline data and measured real-time data of the capacitor to be evaluated and calculates the corresponding equivalent series resistance based on its current data and voltage data. Then, different frequencies are substituted one by one to obtain the impedance curve of the equivalent series resistance with respect to the sampling resolution; during the degradation process of the capacitor, the impedance curve will change, which is specifically reflected in the inflection point and slope of the curve; then, by comparing the baseline impedance curve of the capacitor in a healthy state, the degree of degradation of the capacitor to be evaluated can be judged, and online health status monitoring and accurate evaluation of the capacitor under the operating conditions of power equipment can be realized, which solves the technical problem of low accuracy of the existing health status monitoring technology of metallized film capacitors, which seriously restricts the reliability of status monitoring and life prediction accuracy of metallized film capacitors in high dynamic application scenarios.

[0075] It should be noted that this capacitor health status assessment method based on the inflection point changes of the multi-frequency impedance curve uses the multi-frequency impedance of the impedance curve, which can accurately capture the various degradation modes caused by changes in different sampling resolutions. Based on the inflection point changes of the impedance characteristic curve of the sampling resolution, a quantitative correlation between the impedance curve changes and the health status of the capacitor is obtained through health status indicator data. Through the health status indicator data grading assessment system and intelligent warning threshold setting, not only can the real-time health status of the capacitor to be evaluated be accurately determined, but also early warning of potential faults can be achieved, significantly improving the operational reliability and maintenance efficiency of the DC link capacitor.

[0076] In one embodiment of the present application, the equivalent series resistance corresponding to the sampling resolution is obtained based on the capacitive reactance value and the total impedance of each sampling resolution, including: subtracting the square of the capacitive reactance value corresponding to the sampling resolution from the square of the total impedance of each sampling resolution to obtain the impedance difference of the sampling resolution; and then taking the square root of the impedance difference to obtain the equivalent series resistance corresponding to the sampling resolution.

[0077] It should be noted that the equivalent series resistance formula is used to calculate the equivalent series resistance corresponding to each sampling resolution based on the capacitive reactance value and the total impedance. The equivalent series resistance formula is:

[0078]

[0079] Where ESR(f) is the equivalent series resistance with a sampling resolution of f, Z(f) is the total impedance with a sampling resolution of f, and X(f) is the capacitive reactance with a sampling resolution of f.

[0080] In one embodiment of the present application, the reference impedance curve and the real-time impedance curve are processed separately to obtain reference inflection point data and a reference slope curve corresponding to the reference impedance curve and real-time impedance inflection point data and a real-time impedance slope curve corresponding to the real-time impedance curve, including:

[0081] Determine a reference impedance function according to the reference impedance curve, and determine a real-time impedance function according to the real-time impedance curve;

[0082] The second-order derivative of the reference impedance function is solved to obtain the reference inflection point data; the second-order derivative of the real-time impedance function is solved to obtain the real-time impedance inflection point data;

[0083] Obtaining the parallel resistance value of the capacitor to be evaluated and the series capacitance value of the series resistor, and calculating the slope of the baseline curve between the two adjacent sampling resolutions based on the parallel resistance value, the series capacitance value, and two adjacent sampling resolutions in the baseline impedance curve; and calculating the slope of the real-time curve between the two adjacent sampling resolutions based on the parallel resistance value, the series capacitance value, and two adjacent sampling resolutions in the real-time impedance curve;

[0084] A reference slope curve is constructed based on the slopes of all reference curves with the frequency as the horizontal coordinate and the curve slope as the vertical coordinate; a real-time impedance slope curve is constructed based on the slopes of all real-time curves with the frequency as the horizontal coordinate and the curve slope as the vertical coordinate.

[0085] It should be noted that since the measured equivalent series resistance (ESR) is actually affected by the equivalent resistance of the dielectric part, both the reference impedance function and the real-time impedance function can be expressed using the impedance expression, which is:

[0086]

[0087] Where ESR is the expression of equivalent series resistance in the impedance curve, R P is the parallel resistance of the capacitor, C S is the series capacitance of the series resistor in the capacitor, ω is the angular frequency corresponding to the sampling resolution, ω = 2πf. Solve for the second-order derivative , obtain the inflection point data h of ω, where h is the abscissa of the curve inflection point. The corresponding curve slope is calculated using the curve slope formula based on the parallel resistance value, series capacitance value, and two adjacent sampling resolutions in the benchmark impedance curve or the real-time impedance curve. Since the ESR difference at two different frequencies is as shown in Formula 1, the curve slope formula for calculating the curve slope is obtained based on Formula 1:

[0088]

[0089] The formula for the slope of the curve is:

[0090]

[0091] Where K ESR is the slope of the curve, ω1 is the first sampling resolution of two adjacent sampling resolutions, and ω2 is the second sampling resolution of two adjacent sampling resolutions.

[0092] In one embodiment of the present application, the total slope offset is obtained by calculating based on the data in the reference slope curve and the real-time impedance slope curve, including: calculating the difference between the real-time curve slope of each frequency in the real-time impedance slope curve and the reference curve slope of the corresponding frequency in the reference slope curve to obtain the slope offset of each frequency; and integrating all slope offsets to obtain the total slope offset.

[0093] It should be noted that the slope offset of the frequency is calculated using the slope offset formula. The slope offset formula is: , f' is the frequency of the slope curve, K_measured(f') is the slope of the real-time curve at the f'th frequency, K_baseline(f') is the slope of the baseline curve at the f'th frequency, and ΔK(f') is the slope offset of the f'th frequency. The total slope offset is obtained by integrating all slope offsets using the offset integral formula: Ks=∫Δ , Ks is the total slope offset.

[0094] In one embodiment of the present application, the inflection point offset is calculated based on the baseline inflection point data and the real-time impedance inflection point data, including: subtracting the baseline inflection point data from the real-time impedance inflection point data to obtain the inflection point offset; and dividing the inflection point offset difference by the baseline inflection point data to obtain the inflection point offset.

[0095] It should be noted that the inflection point offset difference Δh is calculated by comparing the real-time impedance inflection point data h_measured of the real-time impedance curve and the baseline inflection point data h_baseline of the baseline impedance curve, that is, Δ The inflection point offset levels for different degrees of degradation are calculated. The inflection point offset level represents the abnormal faults in the conductive and insulating parts. The inflection point offset difference Δh is divided by the baseline inflection point data h_baseline to obtain the inflection point offset hs, that is, hs = Δh / h_baseline.

[0096] In one embodiment of the present application, the capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve includes: dividing the inflection point offset by the inflection point offset setting value to obtain the inflection point offset rate, and subtracting the inflection point offset rate from 1 to obtain the inflection point change; dividing the total slope offset value by the slope offset setting value to obtain the slope curve rate, and subtracting the slope curve rate from 1 to obtain the slope offset change; multiplying the inflection point change by the first weight coefficient to obtain first indicator data, multiplying the slope offset change by the second weight coefficient to obtain second indicator data, and adding the first indicator data and the second indicator data to obtain the health status indicator data of the capacitor to be evaluated.

[0097] It should be noted that, since the degree of influence of the slope curve offset on the degradation of the capacitor reflects the degradation of the metal part of the capacitor, it is necessary to calculate the slope offset change HSI_K, HSI_K=1-Ks / Ks_max, where Ks is the inflection point offset, Ks_max is the inflection point offset setting value, and the inflection point offset setting value refers to the slope curve offset preset value when the capacitor capacitance drops to 95%. Since the degree of influence of the inflection point change on the degradation of the capacitor reflects the abnormal failure of the capacitor, it is necessary to calculate the inflection point change HSI_h, HSI_h=1-hs / hs_max, where hs is the inflection point offset, hs_max is the inflection point offset setting value, and the inflection point offset setting value refers to the inflection point offset preset value when the capacitor capacitance drops to 95%. The formula for calculating the health status index data is HSI=w h *HSI_hs+w K *HSI_K,w h is the first weight coefficient, w K is the first weighting factor, and HSI is the health status index data. In this embodiment, the capacitor health status assessment method based on the inflection point changes of the multi-frequency impedance curve can collect measured real-time data every hour and update the real-time impedance curve. The health status index data HSI is calculated in real time to update the health status of the capacitor to be assessed. In this embodiment, the first and second weighting factors can be set as needed and are not specifically limited here.

[0098] In one embodiment of the present application, determining the health of the capacitor to be evaluated based on the health status indicator data includes:

[0099] If the health status indicator data is less than the first set value and greater than 0, the health status of the capacitor to be evaluated is in a severely degraded state;

[0100] If the health status indicator data is not less than the first set value and less than the second set value, the health status of the capacitor to be evaluated is in a moderately degraded state;

[0101] If the health status indicator data is not less than the second set value and less than the third set value, the health status of the capacitor to be evaluated is in a slightly degraded state;

[0102] If the health status indicator data is not less than the third set value and less than the fourth set value, the health status of the capacitor to be evaluated is in a healthy state.

[0103] It should be noted that the first set value can be set to 0.2, the second set value can be set to 0.5, the third set value can be set to 0.8, and the fourth set value can be set to 1. In this embodiment, when the health status index data HSI = 1, it indicates that the health status of the capacitor to be evaluated is completely healthy; when the health status index data HSI = 0, it indicates that the health status of the capacitor to be evaluated is completely failed and the capacitor to be evaluated is scrapped.

[0104] In an embodiment of the present application, the capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve can use the 24-hour change data of the health status indicator data HSI based on the time series change to linearly regress and predict the remaining life RUL of the capacitor to be evaluated.

[0105] It should be noted that when the health index (HIS) falls below 0.5, the capacitor under evaluation is decommissioned. The HSI of the capacitor under evaluation exhibits roughly linear degradation over time. If the total time required for the HSI to decrease from 0.7 to 0.6 is approximately five months, then the time required for the capacitor under evaluation to decrease from 0.6 to 0.5 is also five months, indicating a remaining lifespan of five months for the capacitor under evaluation.

[0106] Example 2:

[0107] Figure 2 This is a schematic diagram of the framework of the capacitor health status assessment device based on the inflection point change of the multi-frequency impedance curve described in an embodiment of the present application.

[0108] like Figure 2 As shown, the embodiment of the present application provides a capacitor health status assessment device based on the inflection point change of a multi-frequency impedance curve, including a data acquisition module 10, a data processing module 20, a first calculation module 30, a curve construction module 40, a second calculation module 50, a third calculation module 60 and a judgment module 70;

[0109] A data acquisition module 10 is configured to acquire baseline data and measured real-time data of the capacitor to be evaluated, wherein the baseline data and the measured real-time data each include the capacitance value of the capacitor to be evaluated, various sampling resolutions, and the time domain current and time domain voltage of the capacitor to be evaluated obtained based on all sampling resolutions;

[0110] A data processing module 20 is configured to process all time-domain currents and all time-domain voltages using a fast Fourier transform to obtain a frequency-domain current corresponding to each time-domain current and a frequency-domain voltage corresponding to each time-domain voltage;

[0111] A first calculation module 30 is configured to calculate, based on the frequency domain current and frequency domain voltage of each sampling resolution, a total impedance corresponding to the sampling resolution; calculate, based on each sampling resolution and the capacitance value, a capacitive reactance value corresponding to the sampling resolution; and calculate, based on the capacitive reactance value of each sampling resolution and the total impedance, an equivalent series resistance corresponding to the sampling resolution;

[0112] A curve construction module 40 is configured to construct a reference impedance curve based on each sampling resolution and the corresponding equivalent series resistance in the reference data; and to construct a real-time impedance curve based on each sampling resolution and the corresponding equivalent series resistance in the measured real-time data;

[0113] A second calculation module 50 is configured to process the reference impedance curve and the real-time impedance curve respectively to obtain reference inflection point data and a reference slope curve corresponding to the reference impedance curve, and real-time impedance inflection point data and a real-time impedance slope curve corresponding to the real-time impedance curve; obtain an inflection point offset by calculation based on the reference inflection point data and the real-time impedance inflection point data; and obtain a total slope offset by calculation based on the data in the reference slope curve and the real-time impedance slope curve;

[0114] a third calculation module 60 configured to obtain an inflection point offset setting value and a slope offset setting value, calculate an inflection point change based on the inflection point offset and the inflection point offset setting value, calculate a slope offset change based on the total slope offset value and the slope offset setting value, and perform a weighted calculation based on the inflection point change and the slope offset change to obtain health status indicator data of the capacitor to be evaluated;

[0115] The judgment module 70 is used to judge the health status of the capacitor to be evaluated based on the health status indicator data.

[0116] It should be noted that the modules in the apparatus of Example 2 have already been described in the steps of the method of Example 1. The modules of the capacitor health assessment device based on inflection point changes in a multi-frequency impedance curve will not be repeated in this embodiment. In this embodiment, the capacitor health assessment device based on inflection point changes in a multi-frequency impedance curve utilizes a data acquisition module, a data processing module, a first calculation module, a curve construction module, a second calculation module, a third calculation module, and a judgment module to implement real-time dynamic monitoring technology for the capacitor under evaluation, without requiring downtime for testing. The device collects baseline data and measured real-time data of the capacitor under evaluation and calculates the corresponding equivalent series resistance (ESR) based on its current and voltage data. Different frequencies are then substituted in to obtain an impedance curve of the equivalent series resistance with respect to the sampling resolution. As the capacitor degrades, this impedance curve changes, as reflected in the curve's inflection point and slope. By comparing the baseline impedance curve of the healthy capacitor, the degree of degradation of the capacitor under evaluation can be determined, enabling online health monitoring and accurate assessment of capacitors under operating conditions of power equipment.

[0117] In an embodiment of the present application, the third calculation module 60 is also used to divide the inflection point offset by the inflection point offset setting value to obtain the inflection point offset rate, and subtract the inflection point offset rate from 1 to obtain the inflection point change; divide the total slope offset value by the slope offset setting value to obtain the slope curve rate, and subtract the slope curve rate from 1 to obtain the slope offset change; multiply the inflection point change by the first weight coefficient to obtain the first indicator data, multiply the slope offset change by the second weight coefficient to obtain the second indicator data, and add the first indicator data and the second indicator data to obtain the health status indicator data of the capacitor to be evaluated.

[0118] Example 3:

[0119] Figure 3 This is a schematic diagram of the terminal device described in an embodiment of the present application.

[0120] like Figure 3 As shown, an embodiment of the present application provides a terminal device, including a processor and a memory;

[0121] A memory, configured to store program codes and transmit the program codes to a processor;

[0122] The processor is configured to execute the above-mentioned capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve according to the instructions in the program code.

[0123] It should be noted that the processor is configured to execute the steps in the aforementioned embodiment of a method for assessing capacitor health based on changes in the inflection points of a multi-frequency impedance curve according to instructions in the program code. Alternatively, the processor implements the functions of the modules / units in the aforementioned system / device embodiments when executing the computer program.

[0124] For example, a computer program may be divided into one or more modules / units, one or more of which are stored in a memory and executed by a processor to complete the present application. One or more modules / units may be a series of computer program instruction segments capable of performing specific functions, and the instruction segments are used to describe the execution process of the computer program in a terminal device.

[0125] Terminal devices can be computing devices such as desktop computers, laptops, PDAs, and cloud servers. Terminal devices may include, but are not limited to, processors and memory. Those skilled in the art will appreciate that this does not constitute a limitation on terminal devices and may include more or fewer components than shown, or a combination of certain components, or different components. For example, terminal devices may also include input / output devices, network access devices, buses, and the like.

[0126] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0127] Memory can be an internal storage unit of a terminal device, such as a hard drive or memory. It can also be an external storage device, such as a plug-in hard drive, a SmartMedia Card (SMC), a Secure Digital (SD) card, or a flash memory card. Furthermore, memory can include both internal and external storage units. Memory is used to store computer programs and other programs and data required by the terminal device. Memory can also be used to temporarily store data that has been output or is about to be output.

[0128] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0129] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0130] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0131] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0132] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes various media that can store program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0133] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A capacitor health status assessment method based on the inflection point change of a multi-frequency impedance curve, characterized in that: The following steps are involved: Obtaining baseline data and measured real-time data of the capacitor to be evaluated, wherein the baseline data and the measured real-time data both include the capacitance value of the capacitor to be evaluated, various sampling resolutions, and time-domain current and time-domain voltage of the capacitor to be evaluated obtained according to all the sampling resolutions; Processing all the time-domain currents and all the time-domain voltages respectively using fast Fourier transform to obtain a frequency-domain current corresponding to each time-domain current and a frequency-domain voltage corresponding to each time-domain voltage; Calculating based on the frequency domain current and the frequency domain voltage of each sampling resolution to obtain a total impedance corresponding to the sampling resolution; calculating based on each sampling resolution and the capacitance value to obtain a capacitive reactance value corresponding to the sampling resolution; calculating based on the capacitive reactance value of each sampling resolution and the total impedance to obtain an equivalent series resistance corresponding to the sampling resolution; Constructing a reference impedance curve based on each sampling resolution and the corresponding equivalent series resistance in the reference data; constructing a real-time impedance curve based on each sampling resolution and the corresponding equivalent series resistance in the measured real-time data; Processing the reference impedance curve and the real-time impedance curve respectively to obtain reference inflection point data and a reference slope curve corresponding to the reference impedance curve, and real-time impedance inflection point data and a real-time impedance slope curve corresponding to the real-time impedance curve; Calculating the inflection point offset based on the reference inflection point data and the real-time impedance inflection point data; and calculating the total slope offset based on the data in the reference slope curve and the real-time impedance slope curve; Obtaining an inflection point offset setting value and a slope offset setting value, and calculating an inflection point change according to the inflection point offset and the inflection point offset setting value; and calculating a slope offset change according to the slope offset total value and the slope offset setting value; Performing weighted calculation based on the inflection point change and the slope offset change to obtain health status indicator data of the capacitor to be evaluated; The health status of the capacitor to be evaluated is determined according to the health status indicator data.

2. The capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve according to claim 1 is characterized in that: Calculating according to the capacitive reactance value and the total impedance of each sampling resolution to obtain the equivalent series resistance corresponding to the sampling resolution includes: subtracting the square of the capacitive reactance value corresponding to the sampling resolution from the square of the total impedance of each sampling resolution to obtain an impedance difference for the sampling resolution; and then taking the square root of the impedance difference to obtain the equivalent series resistance corresponding to the sampling resolution.

3. The capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve according to claim 1 is characterized in that: Processing the reference impedance curve and the real-time impedance curve separately to obtain reference inflection point data and a reference slope curve corresponding to the reference impedance curve and real-time impedance inflection point data and a real-time impedance slope curve corresponding to the real-time impedance curve includes: Determine a reference impedance function according to the reference impedance curve, and determine a real-time impedance function according to the real-time impedance curve; Solving the second-order derivative of the reference impedance function to obtain reference inflection point data; solving the second-order derivative of the real-time impedance function to obtain real-time impedance inflection point data; Obtaining the parallel resistance value of the capacitor to be evaluated and the series capacitance value of the series resistor, and calculating based on the parallel resistance value, the series capacitance value, and two adjacent sampling resolutions in the reference impedance curve to obtain a reference curve slope between the two adjacent sampling resolutions; and calculating based on the parallel resistance value, the series capacitance value, and two adjacent sampling resolutions in the real-time impedance curve to obtain a real-time curve slope between the two adjacent sampling resolutions; A reference slope curve is constructed based on all the reference curve slopes with frequency as the horizontal coordinate and curve slope as the vertical coordinate; a real-time impedance slope curve is constructed based on all the real-time curve slopes with frequency as the horizontal coordinate and curve slope as the vertical coordinate.

4. The capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve according to claim 1 is characterized in that: Calculating based on the data in the reference slope curve and the real-time impedance slope curve to obtain the total slope offset includes: performing difference calculation on the real-time curve slope of each frequency in the real-time impedance slope curve and the reference curve slope of the corresponding frequency in the reference slope curve to obtain the slope offset of each frequency; integrating all the slope offsets to obtain the total slope offset value.

5. The capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve according to claim 1 is characterized in that: Obtaining the inflection point offset by calculating based on the benchmark inflection point data and the real-time impedance inflection point data includes: subtracting the benchmark inflection point data from the real-time impedance inflection point data to obtain an inflection point offset difference; and dividing the inflection point offset difference by the benchmark inflection point data to obtain an inflection point offset.

6. The capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve according to claim 1 is characterized in that: include: Dividing the inflection point offset by the inflection point offset setting value to obtain an inflection point offset rate, and subtracting the inflection point offset rate from 1 to obtain an inflection point change; The total slope offset value is divided by the slope offset set value to obtain a slope curve rate, and the slope curve rate is subtracted from 1 to obtain a slope offset change; the inflection point change is multiplied by a first weight coefficient to obtain first indicator data, the slope offset change is multiplied by a second weight coefficient to obtain second indicator data, and the first indicator data and the second indicator data are added to obtain health status indicator data of the capacitor to be evaluated.

7. The capacitor health status assessment method based on the inflection point change of the multi-frequency impedance curve according to any one of claims 1 to 6, characterized in that: Determining the health of the capacitor to be evaluated according to the health status indicator data includes: If the health status indicator data is less than the first set value and greater than 0, the health status of the capacitor to be evaluated is in a severely degraded state; If the health status indicator data is not less than the first set value and less than the second set value, the health status of the capacitor to be evaluated is in a moderately degraded state; If the health status indicator data is not less than the second set value and less than the third set value, the health status of the capacitor to be evaluated is in a slightly degraded state; If the health status indicator data is not less than the third set value and less than the fourth set value, the health status of the capacitor to be evaluated is in a healthy state.

8. A capacitor health status assessment device based on the inflection point change of a multi-frequency impedance curve, characterized in that: include: A data acquisition module, a data processing module, a first calculation module, a curve construction module, a second calculation module, a third calculation module and a judgment module; The data acquisition module is configured to acquire baseline data and measured real-time data of the capacitor to be evaluated, wherein the baseline data and the measured real-time data each include the capacitance value of the capacitor to be evaluated, various sampling resolutions, and time-domain current and time-domain voltage of the capacitor to be evaluated obtained according to all the sampling resolutions; The data processing module is configured to process all the time-domain currents and all the time-domain voltages using fast Fourier transform to obtain a frequency-domain current corresponding to each time-domain current and a frequency-domain voltage corresponding to each time-domain voltage; The first calculation module is configured to calculate, based on the frequency domain current and the frequency domain voltage of each sampling resolution, a total impedance corresponding to the sampling resolution; calculate, based on each sampling resolution and the capacitance value, a capacitive reactance value corresponding to the sampling resolution; and calculate, based on the capacitive reactance value of each sampling resolution and the total impedance, an equivalent series resistance corresponding to the sampling resolution; The curve construction module is used to construct a reference impedance curve according to each sampling resolution and the corresponding equivalent series resistance in the reference data; and to construct a real-time impedance curve according to each sampling resolution and the corresponding equivalent series resistance in the measured real-time data; The second calculation module is used to process the reference impedance curve and the real-time impedance curve respectively to obtain reference inflection point data and a reference slope curve corresponding to the reference impedance curve, and real-time impedance inflection point data and a real-time impedance slope curve corresponding to the real-time impedance curve; Obtaining an inflection point offset by calculation based on the reference inflection point data and the real-time impedance inflection point data; Calculating based on the data in the reference slope curve and the real-time impedance slope curve to obtain a total slope offset value; The third calculation module is configured to obtain an inflection point offset setting value and a slope offset setting value, and calculate an inflection point variation based on the inflection point offset and the inflection point offset setting value; and calculate a slope offset variation based on the slope offset total value and the slope offset setting value; Performing weighted calculation based on the inflection point change and the slope offset change to obtain health status indicator data of the capacitor to be evaluated; The judgment module is used to judge the health status of the capacitor to be evaluated according to the health status indicator data.

9. The capacitor health status assessment device based on the inflection point change of the multi-frequency impedance curve according to claim 8, characterized in that: The third calculation module is further configured to divide the inflection point offset by the inflection point offset setting value to obtain an inflection point offset rate, and subtract the inflection point offset rate from 1 to obtain an inflection point change; divide the total slope offset value by the slope offset setting value to obtain a slope curve rate, and subtract the slope curve rate from 1 to obtain a slope offset change; multiply the inflection point change by a first weight coefficient to obtain first indicator data, multiply the slope offset change by a second weight coefficient to obtain second indicator data, and add the first indicator data and the second indicator data to obtain health status indicator data of the capacitor to be evaluated.

10. A terminal device, characterized in that: including a processor and a memory; The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the capacitor health status assessment method based on the inflection point change of a multi-frequency impedance curve according to any one of claims 1 to 7 according to the instructions in the program code.

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