A life prediction method for metallized film capacitors

Abstract

The present invention belongs to the technical field related to capacitor life prediction, and specifically relates to a method for predicting the life of a metallized film capacitor, comprising: performing an aging simulation test on a sample capacitor, wherein after each round of the test, the sample capacitor is cooled and its capacitance is measured, and the capacitance decay value under each round is calculated; when the capacitance decay value and the number of rounds both reach preset values, a linear relationship between the number of rounds and the capacitance decay value is fitted to obtain the round corresponding to when the capacitance decays to a performance deterioration index, and the decay time is obtained based on the round; wherein the preset value corresponding to the capacitance decay value is less than the performance deterioration index; based on the decay time and other simulation experiment parameters and actual operating condition data required by the capacitor failure life evaluation and prediction theoretical model, the capacitor failure life evaluation and prediction theoretical model is used to calculate the life of the metallized film capacitor under actual operating conditions. The present invention can simply and conveniently predict the operating life of the metallized film capacitor.

Description

Technical Field

[0001] The present invention belongs to the technical field related to capacitor life prediction, and more specifically, relates to a method for predicting the life of a metallized film capacitor. Background Art

[0002] Metallized film capacitors are formed by winding a double layer of organic film with a thin metal vapor-deposited on one side. They are widely used in fields such as flexible DC transmission and pulse power. Metallized film capacitors have self-healing properties. When a weak point in the film is broken down, the energy stored in the dielectric there is instantly released and generates heat, evaporating the weak point and the vapor-deposited metal electrodes around it, completing self-healing and restoring insulation. Each self-healing event causes a slight drop in capacitance. After several self-healing events, the capacitance drops significantly. When the capacitance drops to a certain value, it will affect the normal operation of the entire system. Accurately predicting the lifespan of capacitors is an essential issue for assessing the reliability and acceptance of the lifespan of flexible DC transmission or pulse power systems.

[0003] The life of metallized film capacitors is very sensitive to operating conditions, including charging voltage, reversal current, temperature, and charge and discharge frequency. Current research on metallized film life prediction mainly uses probability theory and mathematical statistics related models to collect, analyze and process relevant data on the capacitance of capacitors after charging and discharging to predict the life of capacitors. Previous life prediction methods usually fit the long-term capacitance attenuation data obtained from short-term tests under certain operating conditions (fixed voltage, temperature, etc.), and thus predict the life when the capacitance drops to a certain value. This type of life prediction requires consistent operating parameters such as voltage and temperature, and it is difficult to deduce the life under other operating conditions from the life under a certain operating condition. Summary of the Invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a method for predicting the life of a metallized film capacitor, which aims to provide a simple and convenient method for predicting the operating life of a metallized film capacitor to facilitate engineering applications.

[0005] To achieve the above object, according to one aspect of the present invention, a method for predicting the life of a metallized film capacitor is provided, comprising:

[0006] The sample capacitors were placed in a constant temperature and humidity chamber for aging simulation tests. After each round of testing, the sample capacitors were cooled and their capacitance was measured. Based on the initial and current capacitance of the sample capacitors, the capacitance decay values ​​for each round were calculated.

[0007] When both the capacitance attenuation value and the number of cycles reach the preset values, a linear relationship between the number of cycles and the capacitance attenuation value is obtained by fitting according to the capacitance attenuation values in each cycle. Thus, the number of cycles corresponding to when the capacitance attenuates to the performance deterioration index is obtained, and the attenuation duration is obtained based on this number of cycles; wherein, the preset value corresponding to the capacitance attenuation value is less than the performance deterioration index.

[0008] According to the attenuation duration and other simulation experiment parameters and actual working condition data required by the theoretical model for evaluating and predicting the capacitor failure life, the theoretical model for evaluating and predicting the capacitor failure life is used to calculate the life of the metallized film capacitor under actual working conditions.

[0009] Furthermore, it further includes:

[0010] When the capacitance attenuation value reaches the preset value and the number of cycles does not reach the preset value, the attenuation duration is directly obtained according to the experimental simulation number of cycles corresponding to the performance deterioration index.

[0011] Furthermore, the preset value corresponding to the capacitance attenuation value is 3%, and the performance deterioration index is 5%.

[0012] Furthermore, the theoretical model for evaluating and predicting the capacitor failure life selected is:

[0013]

[0014] In the formula, L w (U w , T ambw ) represents the capacitor failure life when the capacitor operates at the voltage U w and the working environment temperature T ambw during actual operation; L0(U0, T amb0 ) represents the capacitor failure life when the capacitor operates at the voltage U0 and the test environment temperature T amb0 during the simulation experiment, that is, the attenuation duration; P0 represents the capacitor test power during the simulation experiment; P w represents the capacitor working power during actual operation; R th represents the thermal resistance from the hottest point inside the capacitor to the external environment, and its value is set to remain unchanged; k represents a comprehensive test coefficient considering measurement errors and sample consistency, 0 < k < 1; α and β are the capacitor voltage stress index and temperature stress index respectively.

[0015] According to another aspect of the present invention, an electronic device is provided, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, the steps of the method described above are implemented.

[0016] According to another aspect of the present invention, a computer-readable storage medium is provided, which includes a stored computer program, wherein when the computer program is executed by a processor, the device where the storage medium is located is controlled to execute the steps of the above-mentioned method.

[0017] According to another aspect of the present invention, a computer program product is provided, comprising a computer program or instructions, which implement the steps of the method described above when executed by a processor.

[0018] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0019] 1. The present invention proposes a method for predicting the life of a metallized film capacitor, assuming that the capacitance attenuation of the capacitor can characterize the performance degradation of the capacitor and is linear within a certain range (the capacitance attenuation is within a small range). When it exceeds the preset degradation index, it is considered to be failed. Therefore, when the capacitance attenuation value and the number of rounds reach the preset value, the linear relationship between the number of rounds and the capacitance attenuation value is fitted, the number of experimental rounds is reduced, and the life under the test environment is obtained. Furthermore, combined with the theoretical model for evaluating and predicting the failure life of capacitors, the life under actual working conditions can be deduced from the life under a certain working condition. That is, the life under other working conditions can be deduced from the life under a certain working condition. Compared with traditional life prediction methods, there is no need to strictly maintain the consistency between the test and the actual working conditions, which saves test time and cost. It is a simple and convenient method for predicting the operating life of metallized film capacitors for engineering applications.

[0020] 2. This invention proposes a method for predicting the life of metallized film capacitors, using a theoretical model Assuming that the thermal resistance from the hottest point inside the capacitor to the external environment remains unchanged, the life of the metallized film capacitor under the test environment (test voltage, test environment temperature, test power) can be obtained, and the life under actual working conditions (actual working voltage, actual working environment temperature, actual working power) can be deduced, ensuring accuracy while being convenient and quick. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flowchart of a method for predicting the life of a metallized film capacitor provided by an embodiment of the present invention;

[0022] Figure 2 This is a framework diagram of a method for predicting the life of a metallized film capacitor provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0024] Example 1

[0025] A method for predicting the life of metallized film capacitors, such as Figure 1 Shown, including:

[0026] The sample capacitors were placed in a constant temperature and humidity chamber for aging simulation tests. After each round of testing, the sample capacitors were cooled and their capacitance was measured. Based on the initial and current capacitance of the sample capacitors, the capacitance decay values ​​for each round were calculated.

[0027] When both the capacitance decay value and the number of rounds reach preset values, a linear relationship between the number of rounds and the capacitance decay value is fitted based on the capacitance decay values ​​in each round. This provides the round corresponding to when the capacitance decays to the performance deterioration index, and the decay duration is determined based on this round. The preset value corresponding to the capacitance decay value is less than the performance deterioration index.

[0028] Based on the above-mentioned attenuation time and other simulation experimental parameters and actual operating condition data required by the capacitor failure life evaluation and prediction theoretical model, the capacitor failure life evaluation and prediction theoretical model is used to calculate the life of the metallized film capacitor under actual operating conditions.

[0029] This embodiment proposes a method for predicting the lifespan of a metallized film capacitor. It assumes that the capacitance decay of the capacitor can characterize the performance degradation of the capacitor and is linear within a certain range (the capacitance decay amount is within a small range). When a preset degradation index is exceeded, the capacitor is considered to have failed. Therefore, when both the capacitance decay value and the number of cycles reach preset values, a linear relationship between the number of cycles and the capacitance decay value is fitted, the number of experimental cycles is reduced, and the lifespan under the test environment is obtained.

[0030] Furthermore, combined with the theoretical model for capacitor failure life assessment and prediction, the life of metallized film capacitors under test conditions can be used to deduce the life under actual working conditions, that is, the life under certain working conditions can be deduced from the life under other working conditions. Compared with traditional life prediction methods, there is no need to strictly maintain the consistency between the test and the actual working conditions, saving test time and cost. It is a simple and convenient method to predict the operating life of metallized film capacitors for engineering applications.

[0031] As an optimal choice, the theoretical model for capacitor failure life assessment and prediction can be selected:

[0032]

[0033] Where, L w (U w , T ambw ) represents the failure life of the capacitor under the actual operating voltage U w and the operating ambient temperature T ambw ; L0(U0, T amb0 ) represents the failure life of the capacitor under the simulated test voltage U0 and the test ambient temperature T amb0 , that is, the attenuation duration; P0 represents the capacitor test power during the simulated test; P w represents the capacitor operating power during actual operation; R th represents the thermal resistance from the hottest point inside the capacitor to the external environment, and its value is set to remain constant; k represents the comprehensive test coefficient considering measurement errors and sample consistency, 0 < k < 1; α and β are the capacitor voltage stress index and temperature stress index respectively.

[0034] Now, the derivation process of this theoretical model will be described in detail:

[0035] For metallized film capacitors, voltage stress and temperature stress are the main factors affecting the life.

[0036] When the operating temperature is the same (voltage stress changes), the relationship between the expected failure life of the metallized film capacitor and the dielectric field strength satisfies

[0037]

[0038] Where, E0 is the dielectric field strength of the capacitor during the test; E w is the dielectric field strength of the capacitor during actual operation; L0(E0) is the failure life of the capacitor during the test; L w (E w ) is the predicted life of the capacitor during actual operation; α is the capacitor voltage stress index, a constant.

[0039] When the dielectric field strength is the same (temperature changes), the relationship between the expected failure life of the metallized film capacitor and the temperature satisfies

[0040]

[0041] Where, T0 is the internal temperature of the capacitor during the test, T w is the internal temperature of the capacitor during actual operation; β is the temperature stress index.

[0042] For a finished capacitor, it is difficult to obtain the internal hottest point temperature T hs when the shell is closed, and the thermal resistance R th obtained from the temperature rise test can be used.Obtained, that is

[0043] T hs = T amb + P s R th (3)

[0044] In the formula, T amb is the ambient temperature, P s is the power.

[0045] ]Combining formulas (1) to (3), when the equivalent film thickness d of the capacitor dielectric remains unchanged, the capacitor failure life evaluation prediction model satisfies

[0046]

[0047] In the formula, k is a comprehensive test coefficient considering measurement errors and sample consistency, 0 < k < 1, and usually k = 0.95; U0 is the capacitor operating voltage during the test, U0 = E0 × d; T amb0 is the test environment temperature; P0 is the capacitor test power; U w is the capacitor operating voltage during actual operation, U w = E w × d; T ambw is the working environment temperature; P w is the capacitor working power. α and β are the capacitor voltage stress index and temperature stress index respectively, which are parameters related to the capacitor dielectric material and process. For polypropylene, taking the most severe case of similar products, α = 7 and β = 13 can be taken.

[0048] Preferably, the preset value corresponding to the capacitance attenuation value is 3%, and the performance deterioration index is 5%.

[0049] Preferably, it further includes:

[0050] When the capacitance attenuation value reaches the preset value and the number of cycles does not reach the preset value, then directly according to the experimental simulation number of cycles corresponding to the performance deterioration index, the attenuation duration is obtained.

[0051] In a specific implementation, as Figure 2 shown, the method of this embodiment can be described as:

[0052] Assumptions: 1) The capacitance attenuation of the capacitor can characterize the performance deterioration of the capacitor and is linear within a certain range (the capacitance attenuation amount is within a small range, such as 5%), and it is considered to fail when it exceeds the preset deterioration index; 2) The thermal resistance from the hottest point inside the capacitor to the external environment remains unchanged. The specific steps for predicting the capacitor failure life are as follows:

[0053] (1) Measure the initial capacitance C0 of the sample capacitor, connect it to the test power supply, and place it in a thermostatic and humid box;

[0054] (2) Perform aging simulation tests on sample capacitors. For sample capacitors used in MMC, the simulation test is generally divided into three stages: Stage 1, overvoltage operation test; Stage 2, charge and discharge test; Stage 3, overvoltage operation test;

[0055] (3) Cool the sample and measure the sample capacitance C t ;

[0056] (4) Calculate the capacitance attenuation value. If the capacitance attenuation is less than 3% (the specific value needs to be combined with the system's need for capacitor stability, repeat steps (2) and (3); if the capacitance attenuation is ≥3%, check whether the number of test rounds meets the set requirements (determined according to the expected life). If it meets the set requirements, fit the capacitance decay and aging test time relationship curve to obtain the test time L0 (U0, T0) when the capacitance decays to the performance degradation index. If it does not meet the set number of test rounds, directly obtain the test time L0 (U0, T0) when the capacitance decays to the performance degradation index, that is, the failure life of the capacitor under the capacitor operating voltage U0 and the internal temperature T0 of the capacitor during the test;

[0057] (5) According to the test results, combined with the capacitor failure life assessment prediction model described in formula (4), the expected life of the capacitor L is calculated by substituting the data into the data. w (U w ,T w ).

[0058] For example, when the capacitor is an MMC capacitor, since the modular multilevel converter (MMC) is the core equipment of the flexible DC transmission system, the sub-module metallized film capacitor is one of the weak links in the MMC. Therefore, effectively predicting the operating life of the metallized film capacitor is of great significance for improving the operating reliability of the MMC and formulating the system maintenance plan.

[0059] Metallized film capacitors are commonly used as damping capacitors in converter valves in flexible DC transmission systems. This study analyzed failure influencing factors and established a failure assessment prediction model based on their actual operating conditions. Accelerated aging tests were then conducted to determine the capacitance degradation patterns under these conditions. The failure assessment prediction model was then used to calculate the expected lifespan of the capacitors in actual operation. This method can shorten testing time and reduce testing costs.

[0060] Example 2

[0061] The present application also relates to an electronic device, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0062] The electronic device may be a computing device such as a desktop computer, a notebook, a PDA, or a cloud server. The processor may be a central processing unit (CPU), or other general-purpose processors, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The memory may be used to store computer programs and / or modules, and the processor may perform various functions of the electronic device by running or executing the computer programs and / or modules stored in the memory, and calling the data stored in the memory.

[0063] The relevant technical solutions are the same as above and will not be repeated here.

[0064] Example 3

[0065] The present application also relates to a computer-readable storage medium having a computer program stored thereon, which implements the steps of the above method when the computer program is executed by a processor.

[0066] Specifically, the memory may include a high-speed random access memory, and may also include a non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), at least one disk storage device, a flash memory device, or other volatile solid-state storage device.

[0067] The relevant technical solutions are the same as above and will not be repeated here.

[0068] Example 4

[0069] The present invention provides a computer program product or computer program, which includes computer instructions stored in a computer-readable storage medium. A processor of a computer device reads the computer instructions from the computer-readable storage medium and executes the computer instructions, causing the computer device to perform the steps of the method of the above-described embodiment of the present invention.

[0070] The relevant technical solutions are the same as above and will not be repeated here.

[0071] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for predicting the life of a metallized film capacitor, characterized in that: include: The sample capacitors were placed in a constant temperature and humidity chamber for aging simulation tests. After each round of testing, the sample capacitors were cooled and their capacitance was measured. Based on the initial and current capacitance of the sample capacitors, the capacitance decay values ​​for each round were calculated. When both the capacitance decay value and the number of rounds reach preset values, a linear relationship between the number of rounds and the capacitance decay value is fitted based on the capacitance decay values ​​in each round, thereby obtaining the round corresponding to when the capacitance decays to the performance deterioration index, and the decay duration is obtained based on the round; wherein the preset value corresponding to the capacitance decay value is less than the performance deterioration index; According to the attenuation time and other simulation experimental parameters and actual working condition data required by the preset capacitor failure life evaluation and prediction theoretical model, the capacitor failure life evaluation and prediction theoretical model is used to calculate the life of the metallized film capacitor under actual working conditions; The theoretical model for capacitor failure life assessment and prediction is: Where, Indicates the capacitor operating voltage during actual operation , working environment temperature Capacitor failure life under ; Indicates the capacitor operating voltage during the simulation experiment , test environment temperature The failure life of the capacitor under the condition, that is, the attenuation time; Indicates the capacitance test power during the simulation experiment; Indicates the working power of the capacitor during actual operation; It represents the thermal resistance from the hottest point inside the capacitor to the external environment, and its value is set to remain unchanged; It represents the comprehensive test coefficient considering measurement error and sample consistency. ; are the capacitor voltage stress index and temperature stress index, respectively.

2. The method for predicting the life of a metallized film capacitor according to claim 1, wherein: Also includes: When the capacitance attenuation value reaches a preset value and the number of rounds does not reach a preset value, the attenuation duration is obtained directly according to the experimental simulation rounds corresponding to the performance deterioration index.

3. The method for predicting the life of a metallized film capacitor according to claim 1, wherein: The preset value corresponding to the capacitance attenuation value is 3%, and the performance deterioration index is 5%.

4. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 3 are implemented.

5. A computer-readable storage medium, characterized in that The computer-readable storage medium includes a stored computer program, wherein when the computer program is executed by a processor, the device where the storage medium is located is controlled to perform the steps of the method according to any one of claims 1 to 3.

6. A computer program product comprising a computer program or instructions, characterized in that When the computer program or instruction is executed by a processor, the steps of the method according to any one of claims 1 to 3 are implemented.

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