Capacitor health state evaluation method and device based on acoustic emission frequency domain characteristics

Abstract

A kind of metalized film capacitor health state evaluation method, system, medium and equipment based on acoustic emission frequency domain feature, in the method, discharge ultrasonic direct current monitoring experimental circuit and aging test loop are built;Different health degrees of metalized film capacitors are obtained by accelerated aging test, metalized film capacitors in different health states are disassembled and connected to discharge ultrasonic monitoring experimental circuit and fixed acoustic emission sensor;The discharge ultrasonic signal of metalized film capacitor within one hour is collected by oscilloscope;The frequency range corresponding to the highest peak value and the number of peak values in the frequency spectrum are counted, and classification is carried out in each frequency domain feature;The proportion distribution of ultrasonic signal frequency domain feature of metalized film capacitor under different health states is calculated, the relative change rate of frequency domain feature proportion is obtained, the probability of capacitor failure is predicted by using logistic regression model, to realize online monitoring of metalized film capacitor health state.

Description

Technical Field

[0001] This invention relates to the field of metallized film capacitor technology, and in particular to a method, system, dielectric, and device for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics. Background Technology

[0002] Metallized film capacitors, as key components in flexible DC transmission converter valves, provide functions such as reactive power compensation, voltage stability regulation, and power flow control, helping to optimize system stability and power quality while reducing transmission losses and improving system response speed and efficiency. Compared to traditional power capacitors, metallized film capacitors operate under more stringent conditions, with operating electric field strengths several times that of parallel AC capacitors and more than twice that of traditional DC filter capacitors, while also exhibiting higher harmonic content. They also require higher reliability and greater current carrying capacity.

[0003] For metallized film capacitors, IEC standard 60384-17 is used in engineering, with a 5% decrease in capacitance as the failure criterion. Therefore, the error in monitoring the capacitance value of metallized film capacitors cannot exceed 1%. Due to limitations in algorithms and equipment, many studies have struggled to achieve the required monitoring accuracy for metallized film capacitors, resulting in limited practical applications in engineering. Furthermore, some online monitoring methods can affect the system loop. For example, using injection methods to measure capacitance or ESR values ​​introduces harmonics into the system, which is detrimental to stable operation. Therefore, researching more accurate online monitoring methods that minimize system impact is crucial for improving system reliability and safety.

[0004] The information disclosed in the background section is only for enhancing the understanding of the background of this invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] This invention provides a method, system, medium, and device for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics, thereby improving the accuracy and precision of the assessment.

[0006] A method for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics includes:

[0007] Step S1: Construct the discharge ultrasonic DC monitoring experimental circuit and the aging test circuit;

[0008] Step S2: Obtain metallized film capacitors with different health conditions through accelerated aging experiments, disassemble the metallized film capacitors with different health conditions, connect them to the discharge ultrasonic monitoring experimental circuit, and fix the acoustic emission sensor.

[0009] Step S3: In the discharge ultrasonic DC monitoring experimental circuit, a DC voltage is applied across the metallized film capacitor, and the discharge ultrasonic signal of the metallized film capacitor is acquired by an oscilloscope within one hour.

[0010] Step S4: Perform frequency domain analysis on the discharge ultrasonic signal, statistically analyze the frequency range corresponding to the highest peak in the spectrum and the number of peaks, and classify them within each frequency domain feature;

[0011] Step S5: Calculate the proportion distribution of ultrasonic signal frequency domain features of the metallized film capacitor under different health conditions, obtain the relative change rate of the frequency domain feature proportion, and use a logistic regression model to predict the probability of capacitor failure, so as to realize online monitoring and assessment of the health status of the metallized film capacitor.

[0012] In the aforementioned method for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics, step S2 includes:

[0013] Step S2.1: In the accelerated aging test circuit, the test temperature was set to 65℃, the humidity to 45%RH, and the test voltage to 1.4U. N After each 12-hour aging cycle, the capacitance value of the metallized film capacitor is measured using a bridge circuit to obtain metallized film capacitors in different health states.

[0014] Step S2.2: After the metallized film capacitor has aged to different predetermined percentages of health, it is removed and connected to the discharge ultrasonic DC monitoring experimental circuit;

[0015] Step S2.3: Secure the acoustic emitter using an ultrasonic coupling agent and fasteners. The acoustic emitter is positioned at the ground terminal of the metallized film capacitor.

[0016] In the aforementioned method for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics, the selected acoustic transmitter has frequency response characteristics in the 120kHz to 300kHz frequency band, and the amplifier uses a PXPA3 amplifier to amplify the detected discharge ultrasonic signal by 100 times while filtering out noise, thereby improving the signal-to-noise ratio.

[0017] In the aforementioned method for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics, step S3 includes:

[0018] Step S3.1: Apply 1.4U to both ends of the metallized film capacitor. N The DC voltage was maintained, and the monitoring temperature of the discharge ultrasonic DC monitoring experimental circuit was kept constant at 20℃ and the humidity at 45%RH.

[0019] Step S3.2: After the pressure stabilizes, the discharge ultrasonic signal generated by the metallized film capacitor within one hour is acquired using an oscilloscope, and the corresponding data is saved.

[0020] In the aforementioned method for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics, step S4 includes:

[0021] Step S4.1: Perform Fourier transform analysis on the discharge ultrasonic signal to obtain the spectrum.

[0022] Step S4.2: Classify the frequency range corresponding to the highest peak in the spectrum, dividing the frequency domain into three bands: 0-100kHz, 100-200kHz, and greater than 200kHz. The highest peak corresponds to the proportion of discharge signal in these three bands, respectively.

[0023] Step S4.3: Classify the number of peaks in the frequency domain into single peaks and multiple peaks, and count the proportion of single peaks and multiple peaks of the discharge signal within one hour.

[0024] In the aforementioned method for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics, step S5 includes:

[0025] Step S5.1: Collect frequency domain characteristic percentage data for metallized film capacitors under different health states. This data includes the percentage of the frequency range corresponding to the highest peak value and the percentage of peak values. Calculate the relative rate of change of the frequency domain characteristic percentage. The formula for the relative rate of change is: 00%,

[0026] Step S5.2: Use a logistic regression model to build a predictive model for capacitor failure, using the relative rate of change as the input feature and the health status as the target variable. The predictive model outputs the probability P (Y=1) that each sample is in a failure state. The form of the predictive model is as follows:

[0027]

[0028] Where Y is a binary response variable representing the failure state (1 indicates failure, 0 indicates health), X1 and X2 are the relative rates of change of two frequency characteristics, β0 is the intercept term, and β1 and β2 are the coefficients of the characteristics.

[0029] Step S5.3: Set a discrimination threshold. During the monitoring process, the proportion of frequency domain features of the ultrasonic discharge signal is statistically analyzed and compared with historical data. The corresponding rate of change is calculated and the rate of change is used as input data into the prediction model to obtain the probability P(Y=1). By comparing this probability with the set threshold, the health status of the capacitor is judged. If P(Y=1)>threshold, it is judged as a failure; otherwise, it is judged as healthy.

[0030] A health status assessment system for metallized film capacitors based on acoustic emission radio frequency domain characteristics includes,

[0031] An aging test circuit is used to accelerate aging experiments to obtain metallized film capacitors with different health levels.

[0032] An experimental circuit for DC monitoring of discharge ultrasound, used to connect metallized film capacitors under different health conditions;

[0033] An acoustic emission sensor is used to: be fixed to the metallized film capacitor, and the discharge ultrasonic monitoring experimental circuit collects the discharge ultrasonic signal of the metallized film capacitor within one hour;

[0034] The frequency domain analysis unit is used to: perform frequency domain analysis on the discharge ultrasonic signal, statistically analyze the frequency range corresponding to the highest peak in the spectrum and the number of peaks, and classify them within each frequency domain feature;

[0035] The calculation unit is used to: calculate the proportion distribution of ultrasonic signal frequency domain features of metallized film capacitors under different health conditions, obtain the relative change rate of frequency domain feature proportions, and use a logistic regression model to predict the probability of capacitor failure, so as to realize online monitoring and assessment of the health status of metallized film capacitors.

[0036] In the system described, the computing unit is a central processing unit.

[0037] A computer storage medium including computer instructions that, when run on a computer, cause the computer to perform the method.

[0038] An electronic device, the electronic device comprising:

[0039] Memory, processor, and computer programs stored in memory and executable on the processor, wherein,

[0040] The processor implements the method when executing the program.

[0041] Compared with existing technologies, this invention has the following advantages: This invention employs acoustic emission technology as a non-destructive testing method. This method can monitor capacitors under normal operating conditions by real-time acquisition of acoustic emission signals, analyzing the proportion of peak values ​​and the frequency range of these peak values ​​in the frequency domain. Compared with traditional testing methods, this method avoids introducing harmonics and other electrical interference, ensuring that the capacitor's performance is not affected during operation and does not interfere with the normal operation of the system. This non-destructive testing method makes continuous monitoring possible, improving the safety and effectiveness of capacitor health status assessment. This method has high sensitivity, capable of capturing minute changes in the capacitor during operation in real time. By accurately analyzing the proportion of peak values ​​and the frequency range of these peak values ​​in the frequency domain, this method can identify early signs of potential faults. This high-sensitivity detection capability allows for preventative measures to be taken before capacitor degradation becomes apparent, effectively reducing the risk of failure and extending the capacitor's lifespan. This method also has good integrability, enabling efficient integration with existing monitoring systems and equipment. This method requires only the addition of an acoustic emission signal acquisition device and corresponding data processing software to achieve real-time assessment of the health status of metallized film capacitors without major modifications to the existing structure of the power system. This integration process is not only simple and fast but also enhances the system's intelligent monitoring capabilities and the management efficiency of power equipment, contributing to comprehensive equipment health management. As capacitors age, their discharge mechanisms change significantly, manifesting as abrupt shifts in frequency domain characteristics. For example, when the health status approaches 95% C0, the number of peaks and the frequency range in the frequency domain may change significantly, indicating a transition from partial discharge to global breakdown. This change is closely related to electrical stress, material degradation, and a weakening of self-healing capabilities; this method offers high detection accuracy. Attached Figure Description

[0042] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0043] In the attached diagram:

[0044] Figure 1 This is a schematic diagram of the experimental circuit for DC monitoring of discharge ultrasound;

[0045] Figure 2 This is a schematic diagram of the accelerated aging test circuit;

[0046] Figure 3 This is a schematic diagram showing the frequency range corresponding to the highest peak value, which is 0-100kHz.

[0047] Figure 4 This is a schematic diagram showing the frequency range corresponding to the highest peak value of 100-200kHz;

[0048] Figure 5 This is a schematic diagram showing that the frequency range corresponding to the highest peak value is greater than 200kHz;

[0049] Figure 6(a) and Figure 6(b) are schematic diagrams of the classification of the number of peaks in the frequency domain. Figure 6(a) is a schematic diagram of the classification of the number of peaks in the frequency domain as a single peak, and Figure 6(b) is a schematic diagram of the classification of the number of peaks in the frequency domain as multiple peaks.

[0050] Figure 7 This is a schematic diagram showing the distribution of the frequency range corresponding to the highest peak value in the frequency domain;

[0051] Figure 8 This is a schematic diagram showing the distribution of the proportion of peak values ​​in the frequency domain.

[0052] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0053] Specific embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While specific embodiments of the invention are shown in the drawings, it should be understood that the invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0054] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0055] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0056] like Figures 1 to 8As shown, the health status assessment method for metallized film capacitors based on acoustic emission radio frequency domain characteristics includes the following steps:

[0057] Step S1: Construct the discharge ultrasonic DC monitoring experimental circuit and the aging test circuit;

[0058] Step S2: Obtain metallized film capacitors with different health conditions through accelerated aging experiments, disassemble the metallized film capacitors with different health conditions, connect them to the discharge ultrasonic monitoring experimental circuit, and fix the acoustic emission sensor.

[0059] Step S3: In the discharge ultrasonic DC monitoring experimental circuit, a DC voltage is applied across the metallized film capacitor, and the discharge ultrasonic signal of the metallized film capacitor is acquired by an oscilloscope within one hour.

[0060] Step S4: Perform frequency domain analysis on the discharge ultrasonic signal, statistically analyze the frequency range corresponding to the highest peak in the spectrum and the number of peaks, and classify them within each frequency domain feature;

[0061] Step S5: Calculate the proportion distribution of ultrasonic signal frequency domain features of the metallized film capacitor under different health conditions, obtain the relative change rate of the frequency domain feature proportion, and use a logistic regression model to predict the probability of capacitor failure, so as to realize online monitoring and assessment of the health status of the metallized film capacitor.

[0062] In a preferred embodiment of the method for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics, step S2 includes:

[0063] Step S2.1: In the accelerated aging test circuit, the test temperature was set to 65℃, the humidity to 45%RH, and the test voltage to 1.4U. N After each 12-hour aging cycle, the capacitance value of the metallized film capacitor is measured using a bridge circuit to obtain metallized film capacitors in different health states.

[0064] Step S2.2: After the metallized film capacitor has aged to different predetermined percentages of health, it is removed and connected to the discharge ultrasonic DC monitoring experimental circuit;

[0065] Step S2.3: Secure the acoustic emitter using an ultrasonic coupling agent and fasteners. The acoustic emitter is positioned at the ground terminal of the metallized film capacitor.

[0066] In a preferred embodiment of the method for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics, the selected acoustic transmitter has frequency response characteristics in the 120kHz to 300kHz frequency band, and the amplifier uses a PXPA3 amplifier to amplify the detected discharge ultrasonic signal by 100 times while filtering out noise, thereby improving the signal-to-noise ratio.

[0067] In a preferred embodiment of the method for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics, step S3 includes:

[0068] Step S3.1: Apply 1.4U to both ends of the metallized film capacitor. N The DC voltage was maintained, and the monitoring temperature of the discharge ultrasonic DC monitoring experimental circuit was kept constant at 20℃ and the humidity at 45%RH.

[0069] Step S3.2: After the pressure stabilizes, the discharge ultrasonic signal generated by the metallized film capacitor within one hour is acquired using an oscilloscope, and the corresponding data is saved.

[0070] In a preferred embodiment of the method for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics, step S4 includes:

[0071] Step S4.1: Perform Fourier transform analysis on the discharge ultrasonic signal to obtain the spectrum.

[0072] Step S4.2: Classify the frequency range corresponding to the highest peak in the spectrum, dividing the frequency domain into three bands: 0-100kHz, 100-200kHz, and greater than 200kHz. The highest peak corresponds to the proportion of discharge signal in these three bands, respectively.

[0073] Step S4.3: Classify the number of peaks in the frequency domain into single peaks and multiple peaks, and count the proportion of single peaks and multiple peaks of the discharge signal within one hour.

[0074] In a preferred embodiment of the method for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics, step S5 includes:

[0075] Step S5.1: Collect frequency domain characteristic percentage data for metallized film capacitors under different health states. This data includes the percentage of the frequency range corresponding to the highest peak value and the percentage of peak values. Calculate the relative rate of change of the frequency domain characteristic percentage. The formula for the relative rate of change is: 00%,

[0076] Step S5.2: Use a logistic regression model to build a predictive model for capacitor failure, using the relative rate of change as the input feature and the health status as the target variable. The predictive model outputs the probability P (Y=1) that each sample is in a failure state. The form of the predictive model is as follows:

[0077]

[0078] Where Y is a binary response variable representing the failure state (1 indicates failure, 0 indicates health), X1 and X2 are the relative rates of change of two frequency characteristics, β0 is the intercept term, and β1 and β2 are the coefficients of the characteristics.

[0079] Step S5.3: Set a discrimination threshold. During the monitoring process, the proportion of frequency domain features of the ultrasonic discharge signal is statistically analyzed and compared with historical data. The corresponding rate of change is calculated and the rate of change is used as input data into the prediction model to obtain the probability P(Y=1). By comparing this probability with the set threshold, the health status of the capacitor is judged. If P(Y=1)>threshold, it is judged as a failure; otherwise, it is judged as healthy.

[0080] A health status assessment system for metallized film capacitors based on acoustic emission radio frequency domain characteristics includes,

[0081] An aging test circuit is used to accelerate the aging process and obtain metallized film capacitors with different health levels.

[0082] An experimental circuit for DC monitoring of discharge ultrasound is connected to metallized film capacitors under different health conditions.

[0083] An acoustic emission sensor is fixed to the metallized film capacitor, and a discharge ultrasonic monitoring experimental circuit collects the discharge ultrasonic signal of the metallized film capacitor within one hour.

[0084] The frequency domain analysis unit performs frequency domain analysis on the discharge ultrasonic signal, statistically analyzes the frequency range corresponding to the highest peak in the spectrum and the number of peaks, and classifies them within each frequency domain feature.

[0085] The calculation unit calculates the proportion distribution of ultrasonic signal frequency domain features of metallized film capacitors under different health conditions, obtains the relative change rate of frequency domain feature proportions, and uses a logistic regression model to predict the probability of capacitor failure, so as to realize online monitoring and assessment of the health status of metallized film capacitors.

[0086] In one embodiment, in the discharge ultrasonic DC monitoring experimental circuit, a DC source and a 25kΩ protective resistor are connected in series to output a DC voltage. The metallized film capacitor has a rated capacitance of 18μF and a rated voltage of 2.0kV. During the experiment, the metallized film capacitor element is placed in a programmable high and low temperature test chamber (model: EL-10JT) to maintain constant temperature and humidity. A Tektronix high-voltage probe (model: P6015A) is placed in the high-voltage section of the constant temperature chamber to detect the capacitor voltage. A PXR15 sensor is used as the acoustic emitter, arranged at the low-voltage end of the element via a coupling agent and a fixing component. This acoustic sensor has a sensitivity exceeding 60dB between 120kHz and 300kHz, indicating that the ultrasonic sensor has good frequency response characteristics within this range. This frequency band can cover the main frequency band of the ultrasonic signal generated by the self-healing of the metallized film capacitor, and can effectively acquire ultrasonic signals. An amplifier connected to the acoustic sensor features high gain, wide dynamic range, low noise, and high input impedance. It can amplify the detected ultrasonic signal by 100 times while filtering out noise, improving the signal-to-noise ratio. This amplifier can output a maximum signal of 20V under a 50Ω load, which can meet the needs of amplifying ultrasonic signals. An oscilloscope, model Tektronix MDO34, is used to record voltage and acoustic signals. The high-voltage probe and acoustic transmitter are connected to the oscilloscope via signal transmission lines through the amplifier.

[0087] In the accelerated aging test circuit, a DC source and a 25kΩ protective resistor are connected in series to output a DC voltage. The metallized film capacitor has a rated capacitance of 18μF and a rated voltage of 2.0kV. During the experiment, multiple metallized film capacitors are placed in parallel in a programmable high and low temperature test chamber (model: EL-10JT) to maintain constant temperature and humidity.

[0088] In a preferred embodiment of the system, the computing unit is a central processing unit.

[0089] A computer storage medium including computer instructions that, when run on a computer, cause the computer to perform the method.

[0090] An electronic device, the electronic device comprising:

[0091] Memory, processor, and computer programs stored in memory and executable on the processor, wherein,

[0092] The processor implements the method when executing the program.

[0093] In one embodiment, step S2: Obtain metallized film capacitors with different health levels through accelerated aging experiments, and connect them to... Figure 1 The circuit shown is used to fix the acoustic emission sensor.

[0094] Step S2.1: The circuit for the accelerated aging test is as follows Figure 2 As shown, the experimental temperature was set at 65℃, the humidity at 45%RH, and the experimental voltage at 1.4U. N After each 12-hour aging cycle, the capacitance value of the capacitor is measured using a high-precision bridge to obtain the metallized film capacitor elements in different health states.

[0095] Step S2.2: When the capacitor ages to different health levels, such as 99% CO, remove it and connect it to the discharge ultrasonic DC monitoring experimental circuit.

[0096] Step S2.3: Secure the acoustic emitter using a dedicated ultrasonic coupling agent and fasteners. The acoustic emitter is positioned at the ground terminal of the capacitor element. The selected acoustic emitter should have good frequency response characteristics in the 120kHz to 300kHz frequency band to ensure effective acquisition of ultrasonic signals. A PXPA3 amplifier is used, which can amplify the detected ultrasonic signal by 100 times while filtering out noise and improving the signal-to-noise ratio.

[0097] Step S3: Apply a DC voltage across the metallized film capacitor element and acquire the discharge ultrasonic signal of the capacitor over one hour using an oscilloscope.

[0098] Step S3.1: Apply 1.4U to both ends of the metallized film capacitor element. N The DC voltage was maintained, and the experimental monitoring temperature was kept constant at 20℃ and the humidity at 45%RH.

[0099] Step S3.2: After the pressure stabilizes, the discharge ultrasonic signal generated by the metallized film capacitor element within one hour is acquired using an oscilloscope, and the corresponding data is saved.

[0100] Step S4: Perform frequency domain analysis on the discharge ultrasonic signals collected from the capacitor within one hour. Analyze the frequency range corresponding to the highest peak in the spectrum and the number of peaks as two frequency domain features, and classify each feature accordingly.

[0101] Step S4.1: Perform Fourier transform analysis on the discharge ultrasonic signals collected within one hour.

[0102] Step S4.2: Classify the frequency range corresponding to the highest peak in the spectrum, dividing the frequency domain into three bands: 0-100kHz, 100-200kHz, and greater than 200kHz. For example... Figure 3 , Figure 4 , Figure 5 As shown, the highest peaks correspond to 0-100kHz, 100-200kHz, and above 200kHz, respectively. The proportion of discharge signals in these three frequency bands was statistically analyzed to determine their distribution over one hour.

[0103] Step S4.3: Classify the number of peaks in the frequency domain into two cases: single-peak and multi-peak, as shown in Figure 6(a) and Figure 6(b). Statistically calculate the proportion of single-peak and multi-peak discharge signals within one hour.

[0104] Step S5: Calculate the proportion distribution of ultrasonic signal frequency domain features of the metallized film capacitor under different health states, thereby obtaining the relative change rate of the frequency domain feature proportions. Use a logistic regression model to predict the probability of capacitor failure, enabling online monitoring and assessment of the capacitor's health status.

[0105] Step S5.1: Collect frequency domain characteristic proportion data of metallized film capacitors under different health states, and calculate the relative rate of change of the frequency domain characteristic proportion. Relative rate of change formula: 00%.

[0106] Step S5.2: Use a logistic regression model to build a predictive model for capacitor failure. The relative rate of change is used as the input feature, and the health status is used as the target variable. The final model outputs the probability P (Y=1) that each sample is in a failure state. The basic form of logistic regression is:

[0107]

[0108] Where Y is a binary response variable (i.e., failure state, 1 represents failure, 0 represents health). X1 and X2 are the relative rates of change of two frequency characteristics. β0 is the intercept term, and β1 and β2 are the coefficients of the characteristics.

[0109] Step S5.3: Set the discrimination threshold according to actual application requirements. During the monitoring process, the proportion of ultrasonic discharge signal frequency domain characteristics within one hour is statistically analyzed and compared with historical data to calculate the corresponding rate of change. The rate of change is used as input data into the prediction model to obtain the probability P(Y=1). The health status of the capacitor is determined by comparing this probability with the set threshold. If P(Y=1) > threshold, it is judged as a failure; otherwise, it is judged as healthy.

[0110] Example of determining the health status of metallized film capacitors using specific frequency domain characteristic parameters:

[0111] Figure 7This paper presents the distribution of the frequency range corresponding to the peak of acoustic emission signals in the frequency domain for metallized film capacitors under different health conditions. FFT analysis of ultrasonic signals collected at different aging stages shows that when the capacitor is at 100% CO health, the percentage of frequencies corresponding to the peak occurring in the 100kHz-200kHz range is 100%. When the capacitor is at 96%-99% CO, the percentage of frequencies corresponding to the peak in the 100kHz-200kHz range is generally greater than 80%. When the capacitor is close to 95% CO, the percentage of frequencies corresponding to the peak occurring in the 100kHz-200kHz range drops significantly to 60%, with the relative change rate jumping from 2% to 36%. This significant jump in the relative change rate of the frequency range corresponding to the peak in the frequency domain indicates capacitor "degradation."

[0112] Figure 8 This paper presents the distribution of the number of peak values ​​in the frequency domain of acoustic emission signals from metallized film capacitors under different health conditions. FFT analysis of ultrasonic signals collected at different aging stages reveals that when the capacitor is in a 96%-100% CO health state, approximately 80% of the ultrasonic signals in the 20kHz-500kHz frequency range have a single peak, with signals having multiple peaks being relatively few. When the capacitor is close to a 95% CO health state, the proportion of single peaks decreases to 34%. The relative change rate jumps from 12% to 58%. This significant jump in the relative change rate of the number of peak values ​​in the frequency domain indicates capacitor "degradation."

[0113] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. A method for assessing the health status of metallized film capacitors based on acoustic emission radio frequency domain characteristics, characterized in that, Includes the following steps: Step S1: Construct the discharge ultrasonic DC monitoring experimental circuit and the aging test circuit; Step S2: Obtain metallized film capacitors with different health conditions through accelerated aging experiments, disassemble the metallized film capacitors with different health conditions and connect them to the discharge ultrasonic DC monitoring experimental circuit and fix the acoustic emission sensor. Step S3: In the discharge ultrasonic DC monitoring experimental circuit, a DC voltage is applied across the metallized film capacitor, and the discharge ultrasonic signal of the metallized film capacitor is acquired by an oscilloscope within one hour. Step S4: Perform frequency domain analysis on the discharge ultrasonic signal, statistically analyze the frequency range corresponding to the highest peak in the spectrum and the number of peaks, and classify them within each frequency domain feature; Step S5: Calculate the proportion distribution of ultrasonic signal frequency domain features of metallized film capacitor under different health conditions, obtain the relative change rate of frequency domain feature proportion, and use logistic regression model to predict the probability of capacitor failure, so as to realize online monitoring to assess the health status of metallized film capacitor. Step S2 includes, Step S2.1: In the accelerated aging test circuit, the test temperature was set to 65℃, the humidity to 45%RH, and the test voltage to 1.4V. U N After each 12-hour aging cycle, the capacitance value of the metallized film capacitor is measured using a bridge circuit to obtain metallized film capacitors in different health states. Step S2.2: After the metallized film capacitor has aged to different predetermined percentages of health, it is removed and connected to the discharge ultrasonic DC monitoring experimental circuit; Step S2.3: Secure the acoustic emitter using ultrasonic coupling agent and fasteners. The acoustic emitter is positioned at the ground terminal of the metallized film capacitor. Step S4 includes, Step S4.1: Perform Fourier transform analysis on the discharge ultrasonic signal to obtain the spectrum. Step S4.2: Classify the frequency range corresponding to the highest peak in the spectrum, dividing the frequency domain into three bands: 0-100kHz, (100, 200kHz], and greater than 200kHz. Statistically analyze the proportion of discharge signals in these three bands, corresponding to the highest peaks in 0-100kHz, (100, 200kHz], and greater than 200kHz respectively. Step S4.3: Classify the number of peaks in the frequency domain into single peaks and multiple peaks, and count the proportion of single peaks and multiple peaks of the discharge signal within one hour; Step S5 includes, Step S5.1: Collect frequency domain characteristic percentage data for metallized film capacitors under different health states. This data includes the percentage of the frequency range corresponding to the highest peak value and the percentage of peak values. Calculate the relative rate of change of the frequency domain characteristic percentage. The formula for the relative rate of change is: , Step S5.2: Use a logistic regression model to build a predictive model for capacitor failure, using the relative rate of change as the input feature and the health status as the target variable. The predictive model outputs the probability P (Y=1) that each sample is in a failure state. The form of the predictive model is as follows: ， Where Y is a binary response variable representing the failure state (1 indicates failure, 0 indicates health), X1 and X2 are the relative rates of change of two frequency characteristics, β0 is the intercept term, and β1 and β2 are the coefficients of the characteristics. Step S5.3: Set a discrimination threshold. During the monitoring process, the proportion of frequency domain features of ultrasonic discharge signals is statistically analyzed and compared with historical data. The corresponding rate of change is calculated and the rate of change is used as input data into the prediction model to obtain the probability P(Y=1). By comparing this probability with the set threshold, the health status of the capacitor is judged. If P(Y=1)>threshold, it is judged as a failure; otherwise, it is judged as healthy.

2. The method for assessing the health status of a metallized film capacitor based on acoustic emission radio frequency domain characteristics according to claim 1, characterized in that, The selected acoustic transmitter has a frequency response characteristic in the 120kHz to 300kHz frequency band. The amplifier uses a PXPA3 amplifier to amplify the detected discharge ultrasonic signal by 100 times while filtering out noise and improving the signal-to-noise ratio.

3. The method for assessing the health status of a metallized film capacitor based on acoustic emission radio frequency domain characteristics according to claim 1, characterized in that, Step S3 includes... Step S3.1: Apply 1.4 kJ / m² to both ends of the metallized film capacitor. U N The DC voltage was maintained, and the monitoring temperature of the discharge ultrasonic DC monitoring experimental circuit was kept constant at 20℃ and the humidity at 45%RH. Step S3.2: After the pressure stabilizes, the discharge ultrasonic signal generated by the metallized film capacitor within one hour is acquired using an oscilloscope, and the corresponding data is saved.

4. A health status assessment system for metallized film capacitors based on acoustic emission radio frequency domain characteristics, the system being applicable to the method described in any one of claims 1-3, characterized in that, It includes, An aging test circuit is used to accelerate aging experiments to obtain metallized film capacitors with different health levels. An experimental circuit for DC monitoring of discharge ultrasound, used to connect metallized film capacitors under different health conditions; An acoustic emission sensor is used to: be fixed to the metallized film capacitor, and the discharge ultrasonic monitoring experimental circuit collects the discharge ultrasonic signal of the metallized film capacitor within one hour; The frequency domain analysis unit is used to: perform frequency domain analysis on the discharge ultrasonic signal, statistically analyze the frequency range corresponding to the highest peak in the spectrum and the number of peaks, and classify them within each frequency domain feature; The calculation unit is used to: calculate the proportion distribution of ultrasonic signal frequency domain features of metallized film capacitors under different health conditions, obtain the relative change rate of frequency domain feature proportions, and use a logistic regression model to predict the probability of capacitor failure, so as to realize online monitoring and assessment of the health status of metallized film capacitors.

5. The system according to claim 4, characterized in that, The computing unit is the central processing unit.

6. A computer storage medium, characterized in that, The storage medium includes computer instructions that, when executed on a computer, cause the computer to perform the method as described in any one of claims 1-3.

7. An electronic device, characterized in that, The electronic device includes: Memory, processor, and computer programs stored in memory and executable on the processor, wherein, When the processor executes the program, it implements the method as described in any one of claims 1-3.

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