Method, system, medium, and apparatus for evaluating health of a metalized film capacitor

Abstract

A kind of metalized film capacitor health state evaluation method, system, medium and equipment based on audible noise signal analysis, in the method, discharge noise monitoring experimental loop is built;Different health states of metalized film capacitor are disassembled and connected to the discharge noise monitoring experimental loop;AC superimposed voltage experiment is carried out in the discharge noise monitoring experimental loop, the temperature of metalized film capacitor in different health states is kept constant at 25 DEG C during the experiment, after pressurization is completed, 10s noise waveform is collected to obtain noise waveform data, metalized film capacitor is depressurized, and the experiment is stopped;The sound pressure level of metalized film capacitor in different health states is calculated according to the noise waveform data respectively, and FFT analysis is carried out simultaneously to obtain its frequency domain characteristics;The reference value of sound pressure level at the initial running time is obtained, and the classification of health or failure is obtained according to the judgment of the sound pressure level, frequency domain characteristics 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 audible noise signal analysis. Background Technology

[0002] Metallized film capacitors play a crucial role in flexible DC transmission converter valves, primarily for reactive power compensation, voltage stability regulation, and power flow control. These functions help 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 withstand significantly higher electric field strengths during operation, several times that of parallel AC capacitors and more than twice that of traditional DC filter capacitors. Furthermore, metallized film capacitors face higher harmonic content and more stringent technical requirements, such as higher reliability and greater current carrying capacity.

[0003] Currently, the industry primarily relies on whether the remaining capacitance value is below 95% of the original capacitance value to assess the health status of metallized film capacitors. While traditional electrical signal monitoring methods are effective in some cases, they may not fully reflect the actual health status of capacitors under complex operating conditions and high harmonic content, especially under high load and variable operating conditions. Furthermore, some improved monitoring methods proposed to date still suffer from problems such as intrusiveness, low efficiency, and poor economic viability. Therefore, it is necessary to propose an auxiliary method for judging and analyzing the health status of metallized film capacitors based on the discharge noise characteristics during operation.

[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 audible noise signal analysis, thereby improving the accuracy and precision of the assessment.

[0006] A method for assessing the health status of metallized film capacitors based on audible noise signal analysis includes:

[0007] Step S1: Construct the discharge noise monitoring experimental circuit;

[0008] Step S2: Disconnect the metallized film capacitors under different health conditions and connect them to the discharge noise monitoring experimental circuit;

[0009] Step S3: In the discharge noise monitoring experimental circuit, an AC / DC superposition voltage experiment is conducted. During the experiment, the temperature of the metallized film capacitor under different health conditions is kept constant at 25°C. After the voltage is applied, the noise waveform is collected for 10 seconds to obtain the noise waveform data. The voltage of the metallized film capacitor is then reduced, and the experiment is stopped.

[0010] Step S4: Calculate the sound pressure level of the metallized film capacitor under different health conditions based on the noise waveform data, and perform FFT analysis to obtain its frequency domain characteristics.

[0011] Step S5: Obtain the baseline value of the sound pressure level at the initial time of operation, and classify the metallized film capacitor as healthy or failed based on the sound pressure level and frequency domain characteristics.

[0012] In the aforementioned method for assessing the health status of metallized film capacitors based on audible noise signal analysis, step S2 includes:

[0013] Step S2.1: Disassemble the metallized film capacitors with remaining capacitance values ​​of 100% and 95%, representing different health conditions.

[0014] Step S2.2: Connect the metallized film capacitor to the discharge noise monitoring experimental circuit using the device fasteners, and set up the acoustic sensor to perform measurement using the four-point method.

[0015] In the aforementioned method for assessing the health status of metallized film capacitors based on audible noise signal analysis, the measurement distance of the acoustic sensor does not exceed 10cm.

[0016] In the aforementioned method for assessing the health status of metallized film capacitors based on audible noise signal analysis, step S3 includes:

[0017] Step S3.1: First, apply a DC voltage across the metallized film capacitor, then superimpose the 50Hz fundamental voltage, which is the most prevalent in the actual operating conditions of the DC-supported metallized film capacitor.

[0018] Step S3.2: After pressurization is completed, acquire a noise waveform for 10 seconds using the acquisition card and save the noise waveform data, which includes the noise waveform and sound pressure level data.

[0019] In the aforementioned method for assessing the health status of metallized film capacitors based on audible noise signal analysis, step S4 includes:

[0020] Step S4.1: Based on the noise time-domain waveform of the noise waveform data, calculate the sound pressure level of the capacitor noise under different health conditions.

[0021] Step S4.2: Perform frequency domain analysis on the noise time-domain waveforms of metallized film capacitors in different health states to obtain their frequency domain waveforms.

[0022] Step S4.3: After frequency domain analysis, extract the frequency domain amplitude at a frequency f of 50Hz.

[0023] In the aforementioned method for assessing the health status of metallized film capacitors based on audible noise signal analysis, step S5 includes:

[0024] Step S5.1: During actual monitoring, when the metallized film capacitor initially runs, its healthy state is considered to be 100%C0. The noise waveform of the metallized film capacitor during its initial operation is collected by the acoustic sensor and the acquisition card, and its sound pressure level is calculated. This is used as the reference value SPL0. The sound pressure level of the metallized film capacitor with healthy states of 100%C0 and 95%C0 is calculated to obtain the corresponding decrease in sound pressure level from the healthy state to the failure state. This decrease is set as the threshold T of the sound pressure level. SPL ,

[0025] Step S5.2: Perform FFT analysis on the noise waveforms of metallized film capacitors with health states of 100% CO and 95% CO, extract the noise signal amplitude at a frequency of 50Hz, and determine the noise frequency domain amplitude at 95% CO as the minimum threshold T of the frequency domain amplitude. f ,

[0026] Step S5.3: When the detected decrease in sound pressure level exceeds the threshold T SPL Furthermore, the frequency domain amplitude of the noise signal at f=50Hz is less than the minimum threshold T. f If it is not valid, it is considered invalid; otherwise, it is considered valid.

[0027] A health status assessment system for metallized film capacitors based on acoustic emission radio frequency domain characteristics includes,

[0028] The discharge noise monitoring experimental circuit is used to: connect metallized film capacitors under different health conditions to obtain noise waveform data;

[0029] The frequency domain analysis unit is used to: calculate the sound pressure level of the metallized film capacitor under different health conditions based on the noise waveform data, and perform FFT analysis to obtain its frequency domain characteristics.

[0030] The calculation unit is used to classify metallized film capacitors as healthy or unhealthy based on sound pressure level and frequency domain characteristics.

[0031] In the system described, the computing unit is a central processing unit.

[0032] A computer storage medium includes computer instructions that, when run on a computer, cause the computer to perform the method.

[0033] An electronic device, the electronic device comprising:

[0034] Memory, processor, and computer programs stored in memory and executable on the processor, wherein,

[0035] The processor implements the method when executing the program.

[0036] Compared with existing technologies, this invention has the following advantages: From the perspective of the aging mechanism of metallized film capacitors, the reason for the decrease in noise sound pressure level can be comprehensively explained from two aspects: dielectric degradation and changes in vibration characteristics. During normal operation, both the vibration and self-healing discharge phenomena of the capacitor generate noise, which is determined by the mechanical vibration of the internal materials and the electrical characteristics of the dielectric. In a healthy state, the dielectric material can effectively support the electrical performance of the capacitor, and its material properties and internal structure can stably transmit and amplify the mechanical vibrations caused by dielectric breakdown and discharge. These vibrations manifest as an increase in noise sound pressure level in the frequency domain. As the capacitor ages, the dielectric material undergoes a degradation process, including a decrease in the material's mechanical strength and elastic modulus, an increase in dielectric loss, and electrode corrosion. This degradation directly affects the self-healing discharge characteristics of the capacitor, causing changes in the internal discharge process and vibration characteristics of the capacitor. Specifically, aging leads to a decrease in the elastic modulus and material strength of the dielectric material, which weakens the mechanical vibrations generated during the self-healing discharge process, thus reducing the intensity of the noise signal. Dielectric degradation can also lead to a decrease in the breakdown voltage inside the capacitor, reducing discharge efficiency and further weakening the sound pressure level (SPL). Changes in the internal structure of the capacitor caused by aging (such as electrode corrosion or dielectric cracks) alter vibration modes and noise propagation paths. These changes weaken the noise signal originally generated by mechanical vibration, resulting in a lower SPL. Therefore, a decrease in the noise SPL level of a capacitor can serve as an important indicator of its aging condition. By monitoring the noise SPL and frequency domain characteristics (such as the amplitude in the 50Hz frequency domain), the health status of the capacitor can be indirectly assessed. This noise analysis-based method, which comprehensively considers changes in dielectric degradation and vibration characteristics, provides an effective health status assessment.

[0037] This invention is remarkably non-destructive. By monitoring the audible noise emitted by metallized film capacitors during operation, no physical contact or additional signal injection is required. This method can be performed under normal capacitor operating conditions without interfering with the capacitor's operation or performance. Compared to traditional electrical signal monitoring methods, the audible noise-based analysis method completely avoids additional burdens and potential risks during system operation, thus ensuring system stability and long-term capacitor reliability. By analyzing the sound pressure level and frequency domain characteristics of the noise, such as the amplitude in the 50Hz frequency domain, the health status of the metallized film capacitor can be effectively assessed without any negative impact on the metallized film capacitor itself or the overall system operation. This method exhibits superior adaptability under complex operating conditions. In experiments, we conducted various test schemes on the capacitors, and the results all showed that this method can provide consistent and reliable health status assessments under different operating conditions. This includes complex operating conditions such as high harmonic content and high load, where the sound pressure level and frequency domain characteristics of the noise still effectively reflect the actual health status of the capacitor. Compared to traditional electrical signal monitoring methods, this method can more accurately adapt to various complex operating conditions, thus ensuring the stability and accuracy of the assessment results. Due to its wide applicability, this method not only enhances the ability to comprehensively monitor the health status of capacitors, but also improves its reliability and practicality in real-world applications.

[0038] It is highly economical. The cost of monitoring using acoustic sensors is relatively low, and the installation and maintenance costs of acoustic sensors are far lower than those of traditional electrical measuring equipment. This makes this method more cost-effective in practical applications. Through simple and economical acoustic measurement, not only are equipment and maintenance costs reduced, but the total long-term operating expenses are also lowered. In addition, the installation of acoustic sensors does not require complex modifications or interventions to the system, further reducing implementation costs and making this method more economical and practical for large-scale applications. Attached Figure Description

[0039] 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.

[0040] In the attached diagram:

[0041] Figure 1 This is a schematic diagram of a DC-supported metallized film capacitor structure;

[0042] Figure 2 This is a schematic diagram of the discharge noise monitoring experimental circuit;

[0043] Figure 3 This is a schematic diagram of the time-domain waveform of noise;

[0044] Figure 4 This is a schematic diagram of the frequency domain waveform around f=50Hz;

[0045] Figure 5 This is a schematic diagram comparing the sound pressure level of capacitors in different health states;

[0046] Figure 6 This is a schematic diagram comparing the frequency domain amplitude of capacitors in different health states at f=50Hz.

[0047] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0048] 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.

[0049] 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.

[0050] 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.

[0051] like Figures 1 to 6 As shown, the health status assessment method for metallized film capacitors based on audible noise signal analysis includes the following steps:

[0052] Step S1: Construct a discharge noise monitoring experimental circuit. Further, in this circuit, a DC power supply and a 20kΩ resistor combine to output a DC voltage. The AC current output from the programmable harmonic power supply passes through a dry-type intermediate frequency transformer and a DC blocking capacitor to output a power frequency voltage. The DC voltage and power frequency voltage are superimposed and act on a metallized film capacitor element. A microphone (MPA201 model) is fixed using a microphone clamp. The microphone is connected to a data acquisition card (PCIe-9529 model) via a signal transmission line. The data acquisition card is then connected to a computer via another signal transmission line. The computer software can record and analyze the corresponding noise waveforms.

[0053] Step S2: Disconnect the metallized film capacitors in different health states from the discharge noise monitoring experimental circuit;

[0054] Step S3: In the discharge noise monitoring experimental circuit, an AC / DC superposition voltage experiment is conducted. During the experiment, the temperature of the metallized film capacitor under different health conditions is kept constant at 25°C. After the voltage is applied, the noise waveform is collected for 10 seconds to obtain the noise waveform data. The voltage of the metallized film capacitor is then reduced, and the experiment is stopped.

[0055] Step S4: Calculate the sound pressure level of the metallized film capacitor under different health conditions based on the noise waveform data, and perform FFT analysis to obtain its frequency domain characteristics.

[0056] Step S5: Obtain the baseline value of the sound pressure level at the initial time of operation, and classify the metallized film capacitor as healthy or failed based on the sound pressure level and frequency domain characteristics.

[0057] In a preferred embodiment of the method for assessing the health status of metallized film capacitors based on audible noise signal analysis, step S2 includes:

[0058] Step S2.1: Disassemble the metallized film capacitors with remaining capacitance values ​​of 100% and 95%, representing different health conditions.

[0059] Step S2.2: Connect the metallized film capacitor to the discharge noise monitoring experimental circuit using the device fasteners, and set up the acoustic sensor to perform measurement using the four-point method.

[0060] In a preferred embodiment of the method for assessing the health status of metallized film capacitors based on audible noise signal analysis, the measurement distance of the acoustic sensor does not exceed 10cm.

[0061] In a preferred embodiment of the method for assessing the health status of metallized film capacitors based on audible noise signal analysis, step S3 includes:

[0062] Step S3.1: First, apply a DC voltage across the metallized film capacitor, then superimpose the 50Hz fundamental voltage, which is the most prevalent in the actual operating conditions of the DC-supported metallized film capacitor.

[0063] Step S3.2: After pressurization is completed, acquire a noise waveform for 10 seconds using the acquisition card and save the noise waveform data, which includes the noise waveform and sound pressure level data.

[0064] In a preferred embodiment of the method for assessing the health status of metallized film capacitors based on audible noise signal analysis, step S4 includes:

[0065] Step S4.1: Based on the noise time-domain waveform of the noise waveform data, calculate the sound pressure level of the capacitor noise under different health conditions.

[0066] Step S4.2: Perform frequency domain analysis on the noise time-domain waveforms of metallized film capacitors in different health states to obtain their frequency domain waveforms.

[0067] Step S4.3: After frequency domain analysis, extract the frequency domain amplitude at a frequency f of 50Hz. Further, the frequency domain analysis is a Fourier transform analysis.

[0068] In a preferred embodiment of the method for assessing the health status of metallized film capacitors based on audible noise signal analysis, step S5 includes:

[0069] Step S5.1: During actual monitoring, when the metallized film capacitor initially runs, its healthy state is considered to be 100%C0. The noise waveform of the metallized film capacitor during its initial operation is collected by the acoustic sensor and the acquisition card, and its sound pressure level is calculated. This is used as the reference value SPL0. The sound pressure level of the metallized film capacitor with healthy states of 100%C0 and 95%C0 is calculated to obtain the corresponding decrease in sound pressure level from the healthy state to the failure state. This decrease is set as the threshold T of the sound pressure level. SPL ,

[0070] Step S5.2: Perform FFT analysis on the noise waveforms of metallized film capacitors with health states of 100% CO and 95% CO, extract the noise signal amplitude at a frequency of 50Hz, and determine the noise frequency domain amplitude at 95% CO as the minimum threshold T of the frequency domain amplitude. f ,

[0071] Step S5.3: When the detected decrease in sound pressure level exceeds the threshold T SPL Furthermore, the frequency domain amplitude of the noise signal at f=50Hz is less than the minimum threshold T. f If it is not valid, it is considered invalid; otherwise, it is considered valid.

[0072] A health status assessment system for metallized film capacitors based on acoustic emission radio frequency domain characteristics includes,

[0073] The discharge noise monitoring experimental circuit is connected to metallized film capacitors under different health conditions to obtain noise waveform data.

[0074] The frequency domain analysis unit calculates the sound pressure level of the metallized film capacitor under different health conditions based on the noise waveform data, and performs FFT analysis to obtain its frequency domain characteristics.

[0075] The calculation unit classifies metallized film capacitors as healthy or unhealthy based on sound pressure level and frequency domain characteristics.

[0076] In a preferred embodiment of the system, the computing unit is a central processing unit.

[0077] A computer storage medium including computer instructions that, when run on a computer, cause the computer to perform the method.

[0078] An electronic device, characterized in that the electronic device comprises:

[0079] Memory, processor, and computer programs stored in memory and executable on the processor, wherein,

[0080] The processor implements the method when executing the program.

[0081] In one embodiment, step S2: Disassemble the metallized film capacitors in different health states, such as... Figure 1 As shown. The metallized film capacitor elements used in the experiment are arranged in this way within the capacitor unit. Figure 1 A structural diagram of a metallized film capacitor is provided to clarify the "capacitor element." The metallized film sample is attached using fasteners. Figure 2 The discharge noise monitoring experimental circuit shown is shown.

[0082] Step S2.1: Disassemble the metallized film components with different health states of 100% and 95% remaining capacitance values.

[0083] Step S2.2: Connect the metallized film capacitor element to the circuit using the device fasteners, and arrange the acoustic sensor according to "GB / T 28543-2021 Method for Measurement of Noise in Power Capacitors". The "four-point method" is used for measurement. Furthermore, to reduce errors caused by propagation attenuation, the measurement distance is selected as 10cm.

[0084] Step S3: Conduct an AC / DC superposition voltage test according to the national standard GB / T 17702-2021. During the test, maintain the temperature of the capacitor elements at different health levels at a constant 25℃. After the voltage is applied, collect a 10-second noise waveform, then reduce the voltage of the capacitor elements and stop the test.

[0085] Step S3.1: Apply AC / DC voltage superposition according to the national standard GB / T 17702-2021. First, apply DC voltage across the capacitor element, then superimpose the 50Hz fundamental voltage, which is the most prevalent in the actual operating conditions of the DC support capacitor.

[0086] Step S3.2: After pressurization is complete, acquire a noise waveform for 10 seconds using a data acquisition card. Save the corresponding noise waveform and sound pressure level data on the computer. During the experiment, the noise waveform can be observed as follows: Figure 3 As shown.

[0087] Step S4: Calculate the sound pressure level of capacitors in different health states based on the collected noise waveform data. Simultaneously, perform FFT analysis to obtain their frequency domain characteristics.

[0088] Step S4.1: According to Figure 3 The noise time-domain waveform shown is used to calculate the sound pressure level of capacitor noise under different health conditions.

[0089] Step S4.2: Perform frequency domain analysis on the noise time-domain waveforms of capacitors in different health states. Figure 3 The noise time-domain waveform shown is subjected to FFT analysis. Its frequency-domain waveform is obtained as follows: Figure 4 As shown.

[0090] Step S4.3: After frequency domain analysis, extract the frequency domain amplitude at frequency f=50Hz.

[0091] Step S5: Determine and classify the health status of the capacitor based on the sound pressure level and frequency domain characteristics: healthy, failed.

[0092] Step S5.1: Calculate the sound pressure level of capacitors in healthy states of 100% CO and 95% CO. Obtain the corresponding decrease in sound pressure level from the healthy state to the failure state, and set it as the sound pressure level threshold T. SPL .

[0093] Step S5.2: Perform FFT analysis on the noise waveforms of capacitors with healthy states of 100% C0 and 95% C0. Extract the noise signal amplitude at a frequency of 50Hz, and determine the noise frequency domain amplitude of 95% C0 as the minimum threshold T for the frequency domain amplitude. f .

[0094] Step S5.3: During actual monitoring, compare the result with the baseline value at the initial operation time. When a decrease in sound pressure level exceeding T is detected... SPL Furthermore, the frequency domain amplitude of the noise signal at f=50Hz is less than T. f If it fails, it is considered invalid. Otherwise, it is considered healthy.

[0095] Step S6: Obtain the baseline value of the sound pressure level at the initial moment of operation. Monitor the noise during the capacitor's operation in real time, collect the noise waveform, and calculate the current sound pressure level and frequency domain data of the capacitor noise.

[0096] Step S6.1: When the capacitor is initially running, its health status can be considered to be 100% CO. The noise waveform of the capacitor during its initial operation is acquired using an acoustic sensor and a data acquisition card, and its sound pressure level is calculated and used as the reference value SPL0.

[0097] Step S6.2: Monitor the noise signal of the capacitor in real time during operation using the acoustic sensor and acquisition card, obtain the current sound pressure level SPL, compare it with SPL0, and calculate the decrease in sound pressure level.

[0098] Step S6.3: Perform FFT analysis on the noise waveform collected during real-time monitoring to extract the frequency domain amplitude at 50Hz.

[0099] Step S7: Determine the corresponding sound pressure level threshold T based on the noise waveform data statistically obtained from capacitors in different health states. SPL Minimum threshold for frequency domain amplitude T f In actual monitoring, capacitor noise data is collected, its characteristics are analyzed, and compared with a set threshold. If the detected sound pressure level drop exceeds T... SPL And the frequency domain amplitude at f=50Hz is less than T. f If the noise level is high, the capacitor is considered faulty and needs to be disassembled and replaced with a healthy capacitor. Otherwise, the capacitor is considered healthy and continues to operate with regular monitoring. The health status of the metallized film capacitor is estimated by measuring the sound pressure level and amplitude at specific frequencies in the frequency domain, thus providing a basis for monitoring the health status of metallized film capacitors used in engineering. Step 5 determines the preset threshold used for comparison during actual monitoring. Step 6 involves collecting and analyzing the required noise waveforms during actual monitoring and comparing them with the preset thresholds from Step 5 to determine the capacitor's health status.

[0100] Example of using noise characteristic analysis to determine the health status of metallized film capacitors:

[0101] Healthy capacitors and capacitors aged to 94.6% CO were used for testing. An MPA201 microphone was placed at the bottom of the capacitor for measurement. The "four-point method" was used for each measurement. The measurement distance was 10cm. Noise waveforms were recorded within 10 seconds after pressure was applied in each test.

[0102] The rated voltage U of the capacitor N The voltage was 2kV. An application of 1.25U was applied in the experiment. N The DC voltage remained constant, and the 50Hz fundamental frequency, which has the highest content in the actual operating conditions of the DC-supported capacitor, was selected as the experimental condition, with a content of 0.15U. N 0.25U N 0.35U N The corresponding ripple rates (AC voltage / DC voltage) are 12%, 20%, and 28%, respectively. The effective value of the superimposed DC and harmonic voltage is 1.4U. N 1.5U N 1.6U N。

[0103] When the microphone is positioned around the bottom of the capacitor for measurement, the superimposed voltage is 1.4U. N 1.5U N and 1.6U N At that time, both healthy and unhealthy capacitors collected self-healing signals within 10 seconds of noise acquisition. At different ripple rates, the sound pressure level acquired by the audible monitoring of healthy capacitors was higher than that of unhealthy capacitors, with the difference exceeding 1 dB. Figure 5 As shown. T can then be... SPL Set to 1dB.

[0104] When a DC voltage is superimposed on a fundamental voltage with a frequency of 50Hz, according to the electrostatic vibration formula, the second term of the frequency is 50Hz, and the vibration force of this term is proportional to 2U. N U DC For DC-supported power capacitors, U is typically... DC >U N Therefore, the second term (f=50Hz) is larger than the first term (f=100Hz), so the noise in the second frequency component will dominate. Figure 6 It can be seen that, within the allowable error range, the amplitude of the healthy capacitor at f=50Hz conforms to a ratio of 2U. N U DC However, unhealthy capacitors do not meet this standard. This may be because, during the aging process, the electrostatic vibration force on the internal metal foil of the metallized film capacitor changes after multiple self-healing processes. Under superimposed voltages with different ripple rates, the amplitude of healthy capacitors at f=50Hz is higher than that of unhealthy capacitors.

[0105] 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 audible noise signal analysis, characterized in that, Includes the following steps: Step S1: Construct the discharge noise monitoring experimental circuit; Step S2: Disconnect the metallized film capacitors under different health conditions and connect them to the discharge noise monitoring experimental circuit; Step S3: In the discharge noise monitoring experimental circuit, an AC / DC superposition voltage experiment is conducted. During the experiment, the temperature of the metallized film capacitor under different health conditions is kept constant at 25°C. After the voltage is applied, the noise waveform is collected for 10 seconds to obtain the noise waveform data. The voltage of the metallized film capacitor is then reduced, and the experiment is stopped. Step S4: Calculate the sound pressure level of the metallized film capacitor under different health conditions based on the noise waveform data, and perform FFT analysis to obtain its frequency domain characteristics. Step S5: Obtain the baseline value of the sound pressure level at the initial time of operation, and classify the metallized film capacitor as healthy or failed based on the sound pressure level and frequency domain characteristics. Step S2 includes, Step S2.1: Disassemble the metallized film capacitors with remaining capacitance values ​​of 100% and 95%, representing different health conditions. Step S2.2: Connect the metallized film capacitor to the discharge noise monitoring experimental circuit using the device fasteners, and set up the acoustic sensor to perform measurement using the four-point method; Step S3 includes... Step S3.1: First, apply a DC voltage across the metallized film capacitor, then superimpose the 50Hz fundamental voltage, which is the most prevalent in the actual operating conditions of the DC-supported metallized film capacitor. Step S3.2: After pressurization is completed, acquire a noise waveform for 10 seconds using the acquisition card and save the noise waveform data, which includes the noise waveform and sound pressure level data; Step S4 includes, Step S4.1: Based on the noise time-domain waveform of the noise waveform data, calculate the sound pressure level of the capacitor noise under different health conditions. Step S4.2: Perform frequency domain analysis on the noise time-domain waveforms of metallized film capacitors in different health states to obtain their frequency domain waveforms. Step S4.3: After frequency domain analysis, extract the frequency domain amplitude at a frequency f of 50Hz; Step S5 includes, Step S5.1: During actual monitoring, the metallized film capacitor is considered to be in 100% health condition when it first starts operating. C 0. The noise waveform of the metallized film capacitor during its initial operation is acquired using an acoustic sensor and a data acquisition card. The sound pressure level is then calculated and used as a reference value. SPL 0, calculating health status as 100%. C 0.95% C The sound pressure level of a metallized film capacitor with a value of 0 is obtained by measuring the decrease in sound pressure level from a healthy state to a failed state, and this decrease is set as the threshold T of the sound pressure level. SPL , Step S5.2: Set the health status to 100%. C 0.95% C FFT analysis was performed on the noise waveform of the metallized film capacitor with a frequency of 0, and the noise signal amplitude at a frequency of 50Hz was extracted. 95% C The noise frequency domain amplitude of 0 is determined as the lowest threshold T of the frequency domain amplitude. f , Step S5.3: When the detected decrease in sound pressure level exceeds the threshold T SPL Furthermore, the frequency domain amplitude of the noise signal at f=50Hz is less than the minimum threshold T. f If it is not valid, it is considered invalid; otherwise, it is considered valid.

2. The method for assessing the health status of metallized film capacitors based on audible noise signal analysis according to claim 1, characterized in that, The acoustic sensor measures at a distance not exceeding 10cm.

3. A health status assessment system for metallized film capacitors based on acoustic emission radio frequency domain characteristics, the system being applicable to the health status assessment method for metallized film capacitors based on audible noise signal analysis as described in claim 1 or 2, characterized in that, It includes, The discharge noise monitoring experimental circuit is used to: connect metallized film capacitors under different health conditions to obtain noise waveform data; The frequency domain analysis unit is used to: calculate the sound pressure level of the metallized film capacitor under different health conditions based on the noise waveform data, and perform FFT analysis to obtain its frequency domain characteristics. The calculation unit is used to classify metallized film capacitors as healthy or unhealthy based on sound pressure level and frequency domain characteristics.

4. The system according to claim 3, characterized in that, The computing unit is the central processing unit.

5. 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 1-2.

6. 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 1-2.

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