Metallized film capacitor health state assessment method, system, medium and equipment

Abstract

The invention discloses a metallized film capacitor health state assessment method and system based on audible noise signal analysis, a medium and equipment, and the method comprises the steps: building a discharge noise monitoring experiment loop; the metalized film capacitors in different health states are detached and connected to the discharge noise monitoring experiment loop; an alternating current and direct current superposition voltage experiment is carried out in the discharge noise monitoring experiment loop, the temperature of the metallized film capacitor in different health states is kept at 25 DEG C constantly in the experiment process, after pressurization is completed, noise waveforms are collected for 10 s to obtain noise waveform data, and voltage reduction and experiment stopping are carried out on the metallized film capacitor; according to the noise waveform data, respectively calculating sound pressure level levels of the metallized film capacitor in different health states, and simultaneously carrying out FFT analysis to obtain frequency domain characteristics of the metallized film capacitor; and acquiring a reference value of the sound pressure level at the initial operation moment, and judging the health state of the metallized film capacitor according to the sound pressure level and the frequency domain characteristics to obtain health or failure classification.

Description

Technical Field

[0001] The present invention relates to the technical field of metallized film capacitors, and in particular to a method, system, medium and equipment for evaluating the health status of metallized film capacitors based on audible noise signal analysis. Background Art

[0002] Metallized film capacitors play a vital role in flexible DC transmission converter valves, mainly used 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 with traditional power capacitors, metallized film capacitors are subject to significantly higher field strengths during operation, which are several times that of parallel AC capacitors and more than twice that of traditional DC filter capacitors. In addition, metallized film capacitors also face higher harmonic content and more stringent technical indicators, such as higher reliability and greater current carrying capacity.

[0003] At present, the industry's detection of the health status of metallized film capacitors mainly relies on the criterion of whether the residual capacitance value is less than 95% of the original capacitance. Although 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 working conditions. However, some of the improved monitoring methods currently proposed still have problems such as being invasive to the system, inefficient, and not economical, so it is necessary to propose a health status judgment and analysis auxiliary method based on the discharge noise characteristics of metallized film capacitors during operation.

[0004] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the invention

[0005] The present invention provides a method, system, medium and equipment for evaluating the health status of a metallized film capacitor based on audible noise signal analysis, which improves the judgment precision and accuracy.

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

[0007] Step S1, building a discharge noise monitoring experimental circuit;

[0008] Step S2, disassembling the metallized film capacitors in different health states and connecting them to the discharge noise monitoring experimental circuit;

[0009] Step S3, performing an AC / DC superposition voltage experiment in a discharge noise monitoring experimental loop, during which the temperature of the metallized film capacitors in different health states is kept constant at 25° C. After the pressurization is completed, a 10s noise waveform is collected to obtain noise waveform data, the metallized film capacitor is depressurized, and the experiment is stopped;

[0010] Step S4, calculating the sound pressure level of the metallized film capacitor in different health states according to the noise waveform data, and performing FFT analysis to obtain its frequency domain characteristics;

[0011] Step S5, obtaining a reference value of the sound pressure level when it is first put into operation, and determining the health status of the metallized film capacitor according to the sound pressure level and frequency domain characteristics to obtain a classification of healthy or failed.

[0012] In the method for evaluating the health status of a metallized film capacitor based on audible noise signal analysis, step S2 comprises:

[0013] Step S2.1: Disassembling metallized film capacitors in different health states with remaining capacitance values ​​of 100% and 95%,

[0014] Step S2.2: Use device fasteners to connect the metallized film capacitor to the discharge noise monitoring experimental circuit, and arrange the acoustic sensor to take the four-point method for measurement.

[0015] In the method for evaluating the health status of a metallized film capacitor based on audible noise signal analysis, the measuring distance of the acoustic sensor does not exceed 10 cm.

[0016] In the method for evaluating the health status of a metallized film capacitor based on audible noise signal analysis, step S3 comprises:

[0017] Step S3.1: first apply a DC voltage across the metallized film capacitor, and then superimpose the 50Hz fundamental voltage with the largest content in the actual operating conditions of the DC support metallized film capacitor.

[0018] Step S3.2: After the pressurization is completed, the noise waveform lasting 10 seconds is collected through the acquisition card, and the noise waveform data is saved, which includes the noise waveform and the sound pressure level data.

[0019] In the method for evaluating the health status of a metallized film capacitor based on audible noise signal analysis, step S4 comprises:

[0020] Step S4.1: Calculate the sound pressure level of capacitor noise in different health states according to the noise time domain waveform of the noise waveform data.

[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 50 Hz.

[0023] In the method for evaluating the health status of a metallized film capacitor based on audible noise signal analysis, step S5 comprises:

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

[0025] Step S5.2: Perform FFT analysis on the noise waveforms of the metallized film capacitors with health states of 100% C0 and 95% C0, extract the noise signal amplitude at a frequency of 50 Hz, and determine the noise frequency domain amplitude of 95% C0 as the minimum threshold T of the frequency domain amplitude. f ,

[0026] Step S5.3: When the sound pressure level drop is detected to exceed the threshold value T SPL , and the frequency domain amplitude of the noise signal at f=50Hz is less than the minimum threshold T f , it is considered invalid, otherwise, it is considered healthy.

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

[0028] A discharge noise monitoring experimental circuit is used to: connect metallized film capacitors in different health states to obtain noise waveform data;

[0029] A frequency domain analysis unit, which is used to calculate the sound pressure level of the metallized film capacitor in different health states according to the noise waveform data, and perform FFT analysis to obtain its frequency domain characteristics;

[0030] The calculation unit is used to determine the health status of the metallized film capacitor according to the sound pressure level and the frequency domain characteristics to obtain the classification of health or failure.

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

[0032] A computer storage medium includes computer instructions, which, when executed on a computer, cause the computer to execute the method described above.

[0033] An electronic device, comprising:

[0034] A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein:

[0035] When the processor executes the program, the method described is implemented.

[0036] Compared with the prior art, the present invention has the following advantages: from the perspective of the aging mechanism of metallized film capacitors, the reasons for the decrease in the noise sound pressure level can be comprehensively explained from the two aspects of dielectric degradation and vibration characteristic changes. During normal operation, the vibration and self-healing discharge phenomenon of the capacitor will generate noise, which is jointly determined by the mechanical vibration of the internal material 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, which are manifested as an increase in the noise sound pressure level in the frequency domain. As the capacitor ages, the dielectric material will undergo a degradation process, including a decrease in the mechanical strength and elastic modulus of the material, an increase in the loss of the dielectric, and corrosion of the electrode. These degradations directly affect the self-healing discharge characteristics of the capacitor, causing the discharge process and vibration characteristics inside the capacitor to change. Specifically: aging causes the elastic modulus of the dielectric material to decrease, the material strength to decrease, so that the mechanical vibration generated during the self-healing discharge process is weakened, resulting in a decrease in the intensity of the noise signal. The degradation of the dielectric may also lead to a decrease in the breakdown voltage inside the capacitor, weakening the discharge efficiency, and further reducing the sound pressure level of the noise. Changes in the internal structure of the capacitor caused by aging (such as corrosion of the electrode or cracks in the dielectric) will change the vibration mode and noise propagation path. These changes weaken the noise signal originally generated by mechanical vibration and reduce the sound pressure level. Therefore, the decrease in the noise sound pressure level of the capacitor can be used as an important indicator of its aging status. By monitoring 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 capacitor can be indirectly evaluated. This method based on noise analysis takes into account the changes in dielectric degradation and vibration characteristics, and can provide an effective health status assessment.

[0037] The present invention has remarkable non-destructiveness. By monitoring the audible noise emitted by the metallized film capacitor during operation, no physical contact or additional signal injection is required to the capacitor. This method can be carried out under normal operating conditions of the capacitor without causing any interference to the operation and performance of the capacitor. Compared with the traditional electrical signal monitoring method, the analysis method based on audible noise completely avoids the additional burden and potential risks in the operation of the system, thereby ensuring the stability of the system and the long-term reliability of the capacitor. By analyzing the sound pressure level of the noise and its frequency domain characteristics, such as the amplitude of the 50Hz frequency domain, the health status of the metallized film capacitor can be effectively evaluated without any negative impact on the metallized film capacitor itself or the overall operation of the system. The method has excellent adaptability under complex working conditions. In the experiment, we conducted a variety of different test schemes on the capacitor, and the results all showed that the method can provide consistent and reliable health status assessment under different operating conditions. This includes that under complex working conditions such as high harmonic content and high load, the sound pressure level and frequency domain characteristics of the noise can still effectively reflect the actual health status of the capacitor. Compared with the traditional electrical signal monitoring method, the method can more accurately adapt to various complex working conditions, thereby ensuring the stability and accuracy of the evaluation results. Due to its wide adaptability, this method not only enhances the comprehensive monitoring capability of the health status of capacitors, but also improves its reliability and practicality in practical applications.

[0038] Highly economical. The cost of using acoustic sensors for monitoring is relatively low, and the installation and maintenance costs of acoustic sensors are much lower than traditional electrical measuring equipment. This makes this method more economical in practical applications. Through simple and economical acoustic measurements, not only equipment and maintenance costs are reduced, but also the total cost of long-term operation is reduced. In addition, the installation of acoustic sensors does not require complex modifications or interventions to the system, further reducing the implementation cost, making this method more economical and practical in large-scale applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] By reading the detailed description of the preferred specific embodiments below, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The drawings in the specification are only for the purpose of illustrating the preferred embodiments and are not considered to be limitations of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative work. Moreover, the same reference numerals are used to represent the same components throughout the drawings.

[0040] In the attached picture:

[0041] Figure 1 It is a schematic diagram of the structure of a DC support metallized film capacitor;

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

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

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

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

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

[0047] The present invention is further explained below in conjunction with the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0048] The specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0049] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the attached claims.

[0050] To facilitate understanding of the embodiments of the present invention, further explanation will be given below by taking specific embodiments as examples in conjunction with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present invention.

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

[0052] Step S1, build a discharge noise monitoring experimental circuit; further, in the discharge noise monitoring experimental circuit, a DC power supply and a resistor with a resistance of 20kΩ are combined to output a DC voltage; the AC current output by the programmable harmonic power supply is combined through a dry-type medium frequency transformer and a DC isolation capacitor to output an industrial frequency voltage. The DC voltage and the industrial frequency voltage are superimposed on the metallized film capacitor element. The microphone is fixed with a microphone fixture, and the model of the microphone is MPA201. The microphone is connected to the acquisition card via a signal transmission line, and the model of the acquisition card is PCIe-9529. The acquisition card is then connected to the computer via a signal transmission line. The computer software can record and analyze the corresponding noise waveform.

[0053] Step S2, disassembling the metallized film capacitors in different health states and connecting them to the discharge noise monitoring experimental circuit;

[0054] Step S3, performing an AC / DC superposition voltage experiment in a discharge noise monitoring experimental loop, during which the temperature of the metallized film capacitors in different health states is kept constant at 25° C. After the pressurization is completed, a 10s noise waveform is collected to obtain noise waveform data, the metallized film capacitor is depressurized, and the experiment is stopped;

[0055] Step S4, calculating the sound pressure level of the metallized film capacitor in different health states according to the noise waveform data, and performing FFT analysis to obtain its frequency domain characteristics;

[0056] Step S5, obtaining a reference value of the sound pressure level when it is first put into operation, and determining the health status of the metallized film capacitor according to the sound pressure level and frequency domain characteristics to obtain a classification of healthy or failed.

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

[0058] Step S2.1: Disassembling metallized film capacitors in different health states with remaining capacitance values ​​of 100% and 95%,

[0059] Step S2.2: Use device fasteners to connect the metallized film capacitor to the discharge noise monitoring experimental circuit, and arrange the acoustic sensor to take the four-point method for measurement.

[0060] In a preferred implementation of the method for evaluating the health status of a metallized film capacitor based on audible noise signal analysis, the measuring distance of the acoustic sensor does not exceed 10 cm.

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

[0062] Step S3.1: first apply a DC voltage across the metallized film capacitor, and then superimpose the 50Hz fundamental voltage with the largest content in the actual operating conditions of the DC support metallized film capacitor.

[0063] Step S3.2: After the pressurization is completed, the noise waveform lasting 10 seconds is collected through the acquisition card, and the noise waveform data is saved, which includes the noise waveform and the sound pressure level data.

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

[0065] Step S4.1: Calculate the sound pressure level of capacitor noise in different health states according to the noise time domain waveform of the noise waveform data.

[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 the frequency domain analysis, the frequency domain amplitude at the frequency f of 50 Hz is extracted. Further, the frequency domain analysis is Fourier transform analysis.

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

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

[0070] Step S5.2: Perform FFT analysis on the noise waveforms of the metallized film capacitors with health states of 100% C0 and 95% C0, extract the noise signal amplitude at a frequency of 50 Hz, and determine the noise frequency domain amplitude of 95% C0 as the minimum threshold value T of the frequency domain amplitude. f ,

[0071] Step S5.3: When the sound pressure level drop is detected to exceed the threshold value T SPL , and the frequency domain amplitude of the noise signal at f=50Hz is less than the minimum threshold T f , it is considered invalid, otherwise, it is considered healthy.

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

[0073] A discharge noise monitoring experimental circuit, which is connected to metallized film capacitors in different health states to obtain noise waveform data;

[0074] A frequency domain analysis unit, which calculates the sound pressure level of the metallized film capacitor in different health states according to the noise waveform data, and performs FFT analysis to obtain its frequency domain characteristics;

[0075] The calculation unit determines the health status of the metallized film capacitor according to the sound pressure level and the frequency domain characteristics to obtain the classification of health or failure.

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

[0077] A computer storage medium includes computer instructions, which, when executed on a computer, cause the computer to execute the method described.

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

[0079] A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein:

[0080] When the processor executes the program, the method described is implemented.

[0081] In one embodiment, step S2: disassembling metallized film capacitors in different health states, such as Figure 1 The metallized film capacitor elements used in the experiment are arranged and placed in the capacitor unit in this way. Figure 1 The structure diagram of the metallized film capacitor is given to clarify the "capacitor element". The metallized film sample is connected to the Figure 2 The discharge noise monitoring experimental circuit shown.

[0082] Step S2.1: dismantle the metallized film components in different health states with residual capacitance values ​​of 100% and 95%.

[0083] Step S2.2: Use the device fasteners to connect the metallized film capacitor element to the circuit, and arrange the acoustic sensor in accordance with GB / T 28543-2021 Power Capacitor Noise Measurement Method. Use the "four-point method" for measurement. In addition, in order to reduce the error caused by propagation attenuation, the measurement distance is selected as 10cm.

[0084] Step S3: Perform an AC / DC superposition voltage experiment according to the national standard GB / T 17702-2021. During the experiment, the temperature of capacitor elements with different health levels is kept constant at 25°C. After the pressurization is completed, the noise waveform is collected for 10s, the capacitor element is depressurized, and the experiment is stopped.

[0085] Step S3.1: Perform AC and DC voltage superposition and pressure application according to the national standard GB / T 17702-2021. First, apply a DC voltage across the capacitor element, and then superimpose the 50Hz fundamental voltage with the largest content in the actual operating conditions of the DC support capacitor.

[0086] Step S3.2: After the pressurization is completed, the noise waveform is collected for 10 seconds through the acquisition card. The corresponding noise waveform and sound pressure level data are saved on the computer. During the experiment, the noise waveform can be observed as follows: Figure 3 shown.

[0087] Step S4: Calculate the sound pressure levels of capacitors in different health states based on the collected noise waveform data, and perform FFT analysis to obtain its 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 in different health states.

[0089] Step S4.2: Perform frequency domain analysis on the noise time domain waveforms of capacitors in different health states. Figure 3 Perform FFT analysis on the noise time domain waveform shown in the figure. Obtain its frequency domain waveform as shown in the figure. Figure 4 shown.

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

[0091] Step S5: judging and classifying the health status of the capacitor according to the sound pressure level and frequency domain characteristics: healthy or failed.

[0092] Step S5.1: Calculate the sound pressure level of the capacitors in the healthy state of 100% C0 and 95% C0. Obtain the corresponding sound pressure level drop from the healthy state to the failure state, and set it as the threshold value T of the sound pressure level. SPL .

[0093] Step S5.2: Perform FFT analysis on the noise waveforms of the capacitors with 100%C0 and 95%C0 health states. 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 of the frequency domain amplitude. f .

[0094] Step S5.3: During the actual monitoring process, the sound pressure level is compared with the baseline value at the time of initial operation. SPL , and the frequency domain amplitude of the noise signal at f=50Hz is less than T f , it is considered invalid. Otherwise, it is considered healthy.

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

[0096] Step S6.1: When the capacitor is initially running, its health status can be considered to be 100% C0. The noise waveform of the capacitor during initial operation is collected by the acoustic sensor and 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 through the acoustic sensor and the acquisition card, obtain the current sound pressure level SPL, compare it with SPL0, and calculate the drop in the sound pressure level.

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

[0099] Step S7: Determine the corresponding sound pressure level threshold T according to the noise waveform data of capacitors in different health states SPL , minimum frequency domain amplitude threshold T f In the actual monitoring process, the capacitor noise data is collected, the corresponding characteristic analysis is performed, and the data is compared with the set threshold. If the detected sound pressure level drops by more than T SPL , and the frequency domain amplitude at the frequency domain f=50Hz is less than T f , the capacitor is considered to have failed and needs to be disassembled and replaced with a healthy capacitor. Otherwise, the capacitor is considered healthy and continues to operate and is monitored regularly. The health status of the metallized film capacitor is estimated by the sound pressure level of the noise and the amplitude of the specific frequency in the frequency domain, thereby providing a basis for the health status monitoring of the metallized film capacitors used in engineering. Step 5 is to determine the preset threshold for comparison during the actual monitoring process. The content of step 6 is to collect the required noise waveform for extraction and analysis in actual monitoring, and compare it with the threshold preset in step 5 to determine the health status of the capacitor.

[0100] An example of analyzing specific noise characteristics to determine the health status of metallized film capacitors:

[0101] Take a healthy capacitor and a capacitor that has been aged to 94.6% C0 for testing. The microphone model MPA201 is placed at the bottom of the capacitor for measurement. The "four-point method" is used for measurement each time. The measurement distance is selected as 10cm. In each test, the noise waveform within 10s after pressurization is collected.

[0102] Rated voltage of capacitor U N The experiment applied 1.25U N The DC voltage remains unchanged, and the harmonic frequency is selected as the 50Hz fundamental wave with the largest content in the actual operating conditions of the DC support capacitor as the experimental condition, with contents 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 values ​​of the DC and harmonic superimposed voltages are 1.4U N , 1.5U N , 1.6U N。

[0103] When the microphone is placed around the bottom of the capacitor, the superimposed voltage is 1.4U N , 1.5U N and 1.6U N When the self-healing signal is collected by both healthy and unhealthy capacitors within 10 seconds of collecting noise, the sound pressure level collected by the audible sound monitoring of healthy capacitors is greater than that of unhealthy capacitors at different ripple rates, and the difference is higher than 1dB. Figure 5 As shown. Then T SPL Set to 1dB.

[0104] When the DC voltage is superimposed on the fundamental voltage with a frequency of 50Hz, according to the electrostatic force vibration formula, the second term of its frequency is 50Hz, and the vibration force ratio of this term is 2U N U DC For DC support power capacitors, U DC >U N , so the second term (f=50Hz) is larger than the first term (f=100Hz), so the noise of 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 is proportional to 2U N U DC ; However, the unhealthy capacitors do not meet the requirements. This may be because the electrostatic vibration force on the internal metal foil of the metallized film capacitor has changed after multiple self-healing processes during the aging process. Under superimposed voltages with different ripple rates, the amplitude of the healthy capacitors at f=50Hz is higher than that of the unhealthy capacitors.

[0105] Although the embodiments of the present invention are described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments and application fields, and the above specific embodiments are only illustrative and instructive, rather than restrictive. A person of ordinary skill in the art can also make many forms under the guidance of this specification and without departing from the scope of protection of the claims of the present invention, all of which belong to the protection of the present invention.

Claims

1. A method for evaluating the health status of metallized film capacitors based on audible noise signal analysis, characterized in that: The steps include: Step S1, building a discharge noise monitoring experimental circuit; Step S2, disassembling the metallized film capacitors in different health states and connecting them to the discharge noise monitoring experimental circuit; Step S3, performing an AC / DC superposition voltage experiment in a discharge noise monitoring experimental loop, during which the temperature of the metallized film capacitors in different health states is kept constant at 25° C. After the pressurization is completed, a 10s noise waveform is collected to obtain noise waveform data, the metallized film capacitor is depressurized, and the experiment is stopped; Step S4, calculating the sound pressure level of the metallized film capacitor in different health states according to the noise waveform data, and performing FFT analysis to obtain its frequency domain characteristics; Step S5, obtaining a reference value of the sound pressure level when it is first put into operation, and determining the health status of the metallized film capacitor according to the sound pressure level and frequency domain characteristics to obtain a classification of healthy or failed.

2. A method for evaluating the health status of a metallized film capacitor based on audible noise signal analysis according to claim 1, characterized in that: Preferably, the step S2 comprises: Step S2.1: Disassembling metallized film capacitors in different health states with remaining capacitance values ​​of 100% and 95%, Step S2.2: Use device fasteners to connect the metallized film capacitor to the discharge noise monitoring experimental circuit, and arrange the acoustic sensor to take the four-point method for measurement.

3. The method for evaluating the health status of a metallized film capacitor based on audible noise signal analysis according to claim 2, characterized in that: The acoustic sensor can measure distances up to 10cm.

4. The method for evaluating the health status of a metallized film capacitor based on audible noise signal analysis according to claim 1, characterized in that: The step S3 comprises: Step S3.1: first apply a DC voltage across the metallized film capacitor, and then superimpose the 50Hz fundamental voltage with the largest content in the actual operating conditions of the DC support metallized film capacitor. Step S3.2: After the pressurization is completed, the noise waveform lasting 10 seconds is collected through the acquisition card, and the noise waveform data is saved, which includes the noise waveform and the sound pressure level data.

5. The method for evaluating the health status of a metallized film capacitor based on audible noise signal analysis according to claim 1, characterized in that: The step S4 comprises: Step S4.1: Calculate the sound pressure level of capacitor noise in different health states according to the noise time domain waveform of the noise waveform data. 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 50 Hz.

6. The method for evaluating the health status of a metallized film capacitor based on audible noise signal analysis according to claim 1, characterized in that: The step S5 comprises: Step S5.1: During the actual monitoring process, when the metallized film capacitor is initially operated, its health status is considered to be 100% C 0, collect the noise waveform of the metallized film capacitor during initial operation through the acoustic sensor and acquisition card, calculate its sound pressure level, and use it as the benchmark value SPL 0, the calculated health status is 100% C 0, 95% C The sound pressure level of the metallized film capacitor with a sound pressure level of 0 is obtained from the healthy state to the failure state, and the sound pressure level decrease corresponding to the failure state is set as the threshold value T of the sound pressure level. SPL , Step S5.2: Set the health status to 100% C 0, 95% C 0 metallized film capacitor noise waveform FFT analysis, extract the noise signal amplitude at a frequency of 50Hz, and convert 95% C The noise frequency domain amplitude of 0 is determined as the minimum threshold T of the frequency domain amplitude. f , Step S5.3: When the sound pressure level drop is detected to exceed the threshold value T SPL , and the frequency domain amplitude of the noise signal at f=50Hz is less than the minimum threshold T f , it is considered invalid, otherwise, it is considered healthy.

7. A system for evaluating the health status of metallized film capacitors based on acoustic emission frequency domain characteristics, characterized in that: These include, A discharge noise monitoring experimental circuit is used to: connect metallized film capacitors in different health states to obtain noise waveform data; A frequency domain analysis unit, which is used to calculate the sound pressure level of the metallized film capacitor in different health states according to the noise waveform data, and perform FFT analysis to obtain its frequency domain characteristics; The calculation unit is used to determine the health status of the metallized film capacitor according to the sound pressure level and the frequency domain characteristics to obtain the classification of health or failure.

8. The system according to claim 7, characterized in that The computing unit is the central processing unit.

9. A computer storage medium, characterized in that The storage medium includes computer instructions, which, when executed on a computer, enable the computer to execute the method according to any one of claims 1 to 7.

10. An electronic device, characterized in that: The electronic device comprises: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the method according to any one of claims 1 to 7 is implemented.

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