Method and system for evaluating partial discharge degradation of bubble defects at high voltage power module adhesive interfaces

Abstract

The application discloses a partial discharge degradation evaluation method and system for glue-solid interface bubble defects of a high-voltage power module. The method comprises the following steps: obtaining partial discharge signals and interface images of a glue-solid interface of a sample to be tested in a first state without applying a preset temperature cycle and in a second state after applying the preset temperature cycle; taking the first state as a reference, extracting partial discharge parameters and bubble defect parameters respectively, and calculating a partial discharge parameter change rate and a bubble defect parameter change amount; meanwhile, an electric field model containing a bubble defect area is established, an electric field strength parameter is solved, and an electric field strength parameter change rate is calculated; the partial discharge parameter change rate, the bubble defect parameter change amount and the electric field strength parameter change rate are normalized and weighted to obtain a degradation index, and a degradation grade is divided according to the degradation index. The method realizes accurate evaluation of glue-solid interface degradation by combining multi-dimensional characteristic parameters, and improves the reliability of degradation evaluation.

Description

Technical Field

[0001] This application relates to the field of high-voltage power module packaging insulation status assessment technology, specifically to a method and system for assessing partial discharge degradation of bubble defects at the adhesive interface of high-voltage power modules. Background Technology

[0002] High-voltage power modules are widely used in equipment for new energy grid connection, high-voltage direct current transmission, electric vehicle traction, industrial frequency conversion, and energy storage converters. As power electronic equipment develops towards higher voltage, higher frequency, and higher power density, the power module packaging structure is subjected to combined electrical, thermal, and mechanical stresses over a long period of time. The reliability of its packaging insulation is gradually becoming an important factor restricting the long-term stable operation of the module.

[0003] In a typical power module packaging structure, the copper electrode, the silicon gel encapsulation layer, and the ceramic substrate constitute the gel-solid interface and the three-bonding region. This region is characterized by abrupt changes in dielectric constant, differences in the coefficients of thermal expansion of the materials, and discontinuous geometric boundaries, making it a preferred location for interfacial partial discharge and insulation degradation.

[0004] In actual operation, power modules often experience frequent start-stop cycles, load fluctuations, changes in cooling conditions, and changes in ambient temperature, causing the gel-cement interface to repeatedly undergo high and low temperature cycles. Temperature cycling generates periodic thermo-mechanical mismatches between the electrodes, silicon gel, and ceramic substrate, leading to decreased interfacial adhesion, localized debonding, and the formation of micro-gaps and bubble defects. Bubble defects, in turn, introduce significant dielectric discontinuities, enhancing electric field distortion at defect boundaries and even inducing concentrated development of partial discharges.

[0005] Existing methods for assessing the degradation of the bond-to-bond interface primarily focus on single discharge amplitudes, partial discharge initiation voltages, or final breakdown results, lacking a joint assessment of the correlation between the morphology of interfacial bubble defects, interfacial discharge parameters, and the evolution of the electric field / space charge within the bubbles after temperature cycling. Therefore, current technologies struggle to accurately identify early defects at the bond-to-bond interface induced by temperature cycling, and also fail to provide degradation grading results sufficient to support encapsulation insulation lifetime assessment and structural optimization. Summary of the Invention

[0006] The purpose of this application is to provide a method and system for assessing the partial discharge degradation of bubble defects at the cement interface of high-voltage power modules, in order to solve the problems of existing technologies that are difficult to accurately identify early defects at the cement interface induced by temperature cycling, and cannot output degradation grading results that can support the assessment of package insulation life and structural optimization, resulting in insufficient assessment reliability.

[0007] To achieve the above objectives, the technical solution adopted in this application is as follows: A first aspect of this application provides a method for assessing the partial discharge degradation of bubble defects at the cemented interface of a high-voltage power module, comprising: acquiring partial discharge signals and interface images of the cemented interface of the test sample in a first state and a second state; the first state being a state without a preset temperature cycle and the second state being a state with a preset temperature cycle applied; extracting partial discharge parameters based on the partial discharge signals, and determining the rate of change of partial discharge parameters in the second state relative to the first state, using the partial discharge parameters in the first state as a benchmark; segmenting the bubble defect region from the interface image and extracting bubble defect parameters, and determining the amount of change of bubble defect parameters in the second state relative to the first state, using the bubble defect parameters in the first state as a benchmark; establishing an electric field model containing the bubble defect region and solving for the electric field strength parameters, and determining the rate of change of the electric field strength parameters in the second state relative to the first state, using the electric field strength parameters in the first state as a benchmark; normalizing and weighting the rate of change of partial discharge parameters, the amount of change of bubble defect parameters, and the rate of change of electric field strength parameters to obtain a degradation index of the cemented interface and determine the corresponding degradation level.

[0008] In one possible implementation, the test sample includes an electrode, a silicone gel encapsulation layer, and a ceramic substrate, wherein the electrode, silicone gel encapsulation layer, and ceramic substrate intersect on the test sample to form a triple bonding point; the gel-ceramic interface includes a silicone gel-ceramic interface and a silicone gel-electrode interface located in the adjacent region of the triple bonding point.

[0009] In one possible implementation, the method further includes: determining the equivalent stress field of the cement-bonded interface in the second state and extracting the stress peak region, and determining the weak insulation region of the interface based on the spatial overlap between the stress peak region and the bubble defect region.

[0010] In one possible implementation, the stress peak region is composed of a grid region in the equivalent stress field that is not less than a preset stress quantile value; the spatial overlap includes the ratio of the area of ​​the intersection region of the stress peak region and the bubble defect region to the area of ​​the union region of the stress peak region and the bubble defect region; when the spatial overlap is greater than or equal to a preset threshold, the intersection region of the stress peak region and the bubble defect region is determined as the weak interface insulation region.

[0011] In one possible implementation, the partial discharge parameters include the partial discharge initiation voltage, the maximum discharge amplitude, and the number of discharges; the bubble defect parameters include the number of bubbles, the average equivalent diameter, the maximum equivalent diameter, the bubble area ratio, and the bubble connectivity; and the electric field strength parameters include the maximum electric field strength parameters of the bubble defect region.

[0012] In one possible implementation, the rate of change of partial discharge parameters includes the rate of decrease of partial discharge initiation voltage, the rate of increase of maximum discharge amplitude, and the rate of increase of discharge times; the change of bubble defect parameters is the fusion result obtained by normalizing and weighting the parameter changes corresponding to at least two bubble defect parameters; the rate of change of electric field strength parameters includes the rate of change of the maximum electric field strength parameter in the bubble defect region.

[0013] In one possible implementation, the formula for calculating the degradation index includes: D=w1 X1+w2 X2+w3 X3+w4 X4+w5 X5; Where D is the degradation index, X1 is the normalized partial discharge initiation voltage decrease rate, X2 is the normalized maximum discharge amplitude growth rate, X3 is the normalized discharge number growth rate, X4 is the normalized bubble defect parameter change, X5 is the normalized maximum electric field strength parameter change rate, w1 is the first weighting coefficient, w2 is the second weighting coefficient, w3 is the third weighting coefficient, w4 is the third weighting coefficient, w5 is the fifth weighting coefficient, and w1+w2+w3+w4+w5=1.

[0014] In one possible implementation, the preset temperature cycle includes a low temperature section, a high temperature section, a heating section, a cooling section, and at least one constant temperature holding section; the temperature of the low temperature section is between -40℃ and 0℃, the temperature of the high temperature section is between 125℃ and 175℃, the absolute value of the temperature change rate of the heating and cooling sections is between 0.1℃ / min and 15℃ / min, and the holding time of the constant temperature holding section is between 5min and 30min.

[0015] In one possible implementation, the degradation levels are sequentially classified into four levels from low to high according to the degree of degradation: Level 1, Level 2, Level 3, and Level 4. When the degradation index is less than a first threshold, it is determined to be Level 1; when the degradation index is greater than or equal to the first threshold and less than the second threshold, it is determined to be Level 2; when the degradation index is greater than or equal to the second threshold and less than the third threshold, it is determined to be Level 3; and when the degradation index is greater than or equal to the third threshold, it is determined to be Level 4. Wherein, the first threshold is greater than the second threshold, and the second threshold is greater than the third threshold.

[0016] A second aspect of this application provides a partial discharge degradation assessment system for bubble defects at the cement-bonded interface of a high-voltage power module, comprising a temperature cycling assembly, a sample holder, a square wave voltage source, a partial discharge sensor, an image acquisition unit, and a computing device; the temperature cycling assembly is used to apply a preset temperature cycle to the sample to be tested; the sample holder is used to clamp the sample to be tested; the output terminal of the square wave voltage source is connected to the electrode of the sample to be tested mounted on the sample holder; the partial discharge sensor is disposed opposite to the cement-bonded interface of the sample to be tested; the optical axis of the image acquisition unit is oriented towards the cement-bonded interface; the output terminals of the partial discharge sensor and the image acquisition unit are both connected to the computing device; the computing device is configured to perform the partial discharge degradation assessment method for bubble defects at the cement-bonded interface of a high-voltage power module according to the first aspect and any embodiment of the first aspect.

[0017] Compared with the prior art, this application has the following advantages: The partial discharge degradation assessment method for bubble defects at the cement-bonded interface of high-voltage power modules provided in this application acquires partial discharge signals and interface images of the cement-bonded interface of the test sample before and after temperature cycling, respectively, and obtains the change rate of partial discharge parameters and the change amount of bubble defect parameters. Combined with the electric field model of the bubble defect region, the change rate of electric field strength parameters is obtained. Then, the three types of parameters are normalized and weighted to obtain a degradation index and determine the degradation level. This achieves a multi-dimensional comprehensive quantitative assessment of bubble defects at the cement-bonded interface under temperature cycling, can identify early latent defects at the cement-bonded interface, and outputs degradation level results that can be used for packaging insulation life assessment and structural optimization, thereby improving the overall reliability of cement-bonded interface degradation assessment. Attached Figure Description

[0018] Figure 1 A flowchart illustrating a method for evaluating the partial discharge degradation of bubble defects at the cement interface of a high-voltage power module, provided as an embodiment of this application. Figure 2 A partial flowchart of a method for evaluating the partial discharge degradation of bubble defects at the cement interface of a high-voltage power module, provided for an embodiment of this application; Figure 3 A partial flowchart of a method for evaluating the partial discharge degradation of bubble defects at the cement interface of a high-voltage power module, provided for an embodiment of this application; Figure 4 A schematic diagram of an interface image segmentation bubble defect region provided in an embodiment of this application; Figure 5 This is a structural block diagram of a partial discharge degradation assessment system for bubble defects at the cement interface of a high-voltage power module, provided in an embodiment of this application. Detailed Implementation

[0019] The present application will now be further described with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application and should not be construed as limiting the scope of protection of the present application. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present application.

[0020] The acquisition, transmission, storage, use, and processing of data in this application comply with relevant national laws and regulations. In the embodiments of this application, certain existing industry solutions such as software, components, and models may be mentioned. These should be considered exemplary, intended only to illustrate the feasibility of implementing the technical solution of this application, and do not imply that the applicant has already used or necessarily used such solutions.

[0021] All terms used in this application have the same meaning as understood by one of ordinary skill in the art to which this application pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and not as idealized or highly formalized, unless expressly defined herein.

[0022] Example 1; See Figures 1 to 3 This application provides a method for evaluating the partial discharge degradation of bubble defects at the cement interface of a high-voltage power module. Figure 1 This shows the main process of degradation assessment consisting of steps S11 to S15. Figure 2 This illustrates the process for identifying weak areas in interface insulation as described in step S16. Figure 3 The degradation level determination process consisting of steps S51 to S54 is shown. Each operation can be performed in the following order, or the signal processing, image processing, and model solving operations can be performed in parallel provided that the data dependencies are satisfied.

[0023] Step S11: Acquire the partial discharge signal and interface image of the cement-solid interface of the test sample in the first and second states. The first state is the state without a preset temperature cycle, and the second state is the state with a preset temperature cycle applied.

[0024] It should be noted that, in the embodiments of this application, the test sample refers to the test object used to simulate or characterize the packaging structure of a high-voltage power module; the high-voltage power module refers to the packaged device that realizes power conversion or switching control under high voltage and high power conditions; the adhesive interface refers to the interface where the insulating packaging material contacts the conductive electrode or insulating substrate after curing and forms an adhesive relationship; the first state refers to the reference state when the test sample has not yet been subjected to a preset temperature cycle; the second state refers to the aging state of the same test sample after being subjected to a preset temperature cycle.

[0025] In one possible implementation, the test sample includes an electrode, a silicone gel encapsulation layer, and a ceramic substrate, wherein the electrode, silicone gel encapsulation layer, and ceramic substrate intersect on the test sample to form a triple bonding point; the gel-ceramic interface includes a silicone gel-ceramic interface and a silicone gel-electrode interface located in the adjacent region of the triple bonding point.

[0026] In one possible implementation, the preset temperature cycle includes a low temperature section, a high temperature section, a heating section, a cooling section, and at least one constant temperature holding section; the temperature of the low temperature section is between -40℃ and 0℃, the temperature of the high temperature section is between 125℃ and 175℃, the absolute value of the temperature change rate of the heating and cooling sections is between 0.1℃ / min and 15℃ / min, and the holding time of the constant temperature holding section is between 5min and 30min.

[0027] In one possible implementation, a UHF (Ultra High Frequency) sensor is used to acquire partial discharge signals; in another possible implementation, a coupling capacitor, current transformer, or electromagnetic near-field probe is used to acquire partial discharge signals, and a microscope, industrial camera, or tomographic imaging device is used to acquire interface images.

[0028] For example, in one specific embodiment, a test sample having a copper electrode, a silicone gel encapsulation layer, and a ceramic substrate is selected, and the area near the three junction points at the edge of the copper electrode is set as a fixed observation area. A square wave voltage with a frequency of 10 kHz, a pulse width of 20 μs, and rise and fall times of 500 ns is used to excite the test sample. A UHF (Ultra High Frequency) sensor with a working bandwidth of 200 MHz to 2 GHz and a high-speed acquisition device with a sampling rate of not less than 2.5 GS / s are used to record the partial discharge signal, while simultaneously acquiring interface images under the same scale and field of view. First, first-state data is acquired without applying a preset temperature cycle. Then, 500 preset temperature cycles are applied, including a low temperature of -30℃, a high temperature of 150℃, a heating rate and a cooling rate of 10℃ / min, and a high-temperature holding time and a low-temperature holding time of 10 min. Second-state data is acquired after the 100th, 200th, 300th, 400th, and 500th cycles.

[0029] In this embodiment of the application, by acquiring data from two states under the same measurement link, the same voltage conditions, and the same observation area, a comparable benchmark-aging paired sample can be formed, reducing the impact of sensor position, imaging scale, and external noise differences on degradation judgment.

[0030] Step S12: Extract partial discharge parameters based on partial discharge signals, and determine the rate of change of partial discharge parameters in the second state relative to the first state, using the partial discharge parameters in the first state as a benchmark.

[0031] In one possible implementation, partial discharge parameters include partial discharge initiation voltage, maximum discharge amplitude, and number of discharges. The partial discharge initiation voltage refers to the applied voltage at which a continuous and repeatable partial discharge pulse is first detected within a specified boosting method and observation time. The maximum discharge amplitude refers to the maximum amplitude of the partial discharge pulse after gain and range calibration within the statistical period. The number of discharges refers to the number of valid pulses exceeding the pulse identification threshold and meeting the pulse interval criterion within the statistical period. The rate of change of partial discharge parameters includes the rate of decrease in partial discharge initiation voltage, the rate of increase in maximum discharge amplitude, and the rate of increase in the number of discharges, respectively reflecting the decrease in the discharge trigger threshold, the increase in the intensity of a single discharge, and the increase in the frequency of discharge activity.

[0032] In this embodiment, a phase-resolved partial discharge (PRPD) map is generated by preprocessing the partial discharge signal to extract the partial discharge parameters. The signal preprocessing includes using an LC (Inductor-Capacitor) high-pass filter to suppress low-frequency background, performing multi-scale decomposition using Symlet wavelets, thresholding the wavelet coefficients, and reconstructing the time-domain signal. The PRPD map is used to correlate pulse amplitude and pulse count with the rising edge, steady-state segment, or falling edge of a square wave period.

[0033] Calculating relative changes based on the first state can mitigate initial differences in the test samples and highlight degradation caused by preset temperature cycling. In one possible implementation, the formulas for calculating the partial discharge initiation voltage drop rate, the maximum discharge amplitude growth rate, and the discharge number growth rate are respectively: KU=(U0-UN) / U0; KA=(AN-A0) / A0; KC=(CN-C0) / C0; where KU is the partial discharge initiation voltage drop rate, KA is the maximum discharge amplitude growth rate, KC is the discharge number growth rate, U0 and UN are the partial discharge initiation voltages in the first and second states, respectively, A0 and AN are the maximum discharge amplitudes in the first and second states, respectively, and C0 and CN are the discharge numbers in the first and second states, respectively. In another possible implementation, outlier removal and mean or median statistics are first performed on multiple repeated test results before calculating the partial discharge parameter change rate.

[0034] For example, in one specific implementation, the original partial discharge signal is sequentially subjected to LC (Inductor-Capacitor) high-pass filtering at a cutoff frequency of 20 MHz, five-layer Symlet wavelet decomposition, soft thresholding, and signal reconstruction to generate a PRPD (Phase Resolved Partial Discharge) map based on the square wave voltage period. The partial discharge initiation voltage, maximum discharge amplitude, and discharge count in the first state are 8.0 kV, 12 mV, and 100 times, respectively, while the corresponding parameters in the second state are 6.8 kV, 18 mV, and 170 times, respectively. Based on this, the partial discharge initiation voltage decrease rate is 0.15, the maximum discharge amplitude increase rate is 0.50, and the discharge count increase rate is 0.70.

[0035] Step S13: Segment the bubble defect region from the interface image and extract the bubble defect parameters. Using the bubble defect parameters in the first state as a reference, determine the change in bubble defect parameters in the second state relative to the first state.

[0036] It should be noted that, in the embodiments of this application, image segmentation refers to the process of distinguishing bubble defect pixels from non-bubble area pixels based on grayscale, texture, edge or learned features; bubble defect area refers to the projection area in the interface image of gas-filled holes, air gaps or interconnected cavities within the cement-solid interface.

[0037] In one possible implementation, bubble defect parameters include the number of bubbles, average equivalent diameter, maximum equivalent diameter, bubble area ratio, and bubble connectivity. The number of bubbles refers to the number of independent bubble defect regions after being labeled with connected components. The equivalent diameter refers to the diameter of a circle with the same projected area as the bubble defect region. The bubble area ratio refers to the ratio of the sum of the areas of all bubble defect regions to the area of ​​the Region of Interest (ROI), where the ROI is a fixed observation area selected based on three junction points and maintaining consistent position and size between the first and second states. Bubble connectivity is a quantitative indicator characterizing the evolution of adjacent bubbles from an isolated state to contact, merging, or forming a continuous channel. The change in bubble defect parameters refers to the fusion result obtained by normalizing and weighting the changes of at least two bubble defect parameters. By fixing the observation area, image registration, and scale calibration, the increase in the number of bubbles, the expansion of their size, and the connectivity trend can be made to correspond one-to-one with preset temperature cycle nodes.

[0038] In one possible implementation, background correction, contrast enhancement, adaptive threshold segmentation, morphological closing operation, hole filling, and connected component labeling are performed sequentially; in another possible implementation, a bubble defect probability map is output using a pixel-based image segmentation model, and then a bubble defect binary mask is formed according to the confidence threshold.

[0039] For example, in one specific implementation, a second-state interface image is segmented, such as... Figure 4 As shown, four bubbles were obtained; the equivalent diameter of bubble 1 is 0.077 mm, the equivalent diameter of bubble 2 is 0.157 mm, the equivalent diameter of bubble 3 is 0.200 mm, and the equivalent diameter of bubble 4 is 0.083 mm; the average equivalent diameter is 0.129 mm, and the maximum equivalent diameter is 0.200 mm.

[0040] Step S14: Establish an electric field model for the region containing bubble defects and solve for the electric field strength parameters. Using the electric field strength parameters of the first state as a reference, determine the rate of change of the electric field strength parameters of the second state relative to the first state.

[0041] It should be noted that, in the embodiments of this application, the electric field model refers to a numerical calculation model established based on the geometric structure of the test sample, the electrical parameters of the material, the electrode potential boundary conditions, and the boundary of the bubble defect region; wherein, the geometric structure of the test sample includes the conductive electrode, the silicon gel encapsulation layer, the ceramic substrate, and their relative positions; the electrical parameters of the material include the relative permittivity, conductivity, and interface charge parameters; the electrode potential boundary conditions include the square wave voltage applied by the high-voltage electrode and the zero potential of the ground electrode; the boundary of the bubble defect region includes the actual contour obtained by segmenting the interface image and the circular or elliptical equivalent contour composed of the equivalent diameter; the model mesh refers to the set of computational units formed by discretizing the continuous geometric region.

[0042] In one possible implementation, the electric field strength parameter includes the maximum electric field strength parameter at the boundary of the bubble defect region or in the region near the three junction points; the rate of change of the electric field strength parameter refers to the relative increase of the maximum electric field strength parameter in the second state relative to the maximum electric field strength parameter in the first state.

[0043] Introducing the measured bubble defect profile into the electric field model allows the electric field distortion location and bubble morphology to share a common spatial origin, and provides a physical quantity reflecting dielectric discontinuities for the degradation index. In one possible implementation, the steady-state electrostatic field at a given electrode potential is solved; in another possible implementation, the space charge migration, accumulation, and dissipation processes are solved jointly, and the transient maximum electric field intensity parameter is extracted within a preset time window at the rising or falling edge of the square wave.

[0044] For example, in one specific implementation, the bubble defect contours of the first and second states are mapped to a two-dimensional electric field model according to the interface image calibration ratio. The copper electrode is set as the high-voltage boundary, and the opposite electrode is set as the ground boundary. The relative permittivity of air, silicon gel, and ceramic substrate are assigned respectively. After local mesh refinement of the bubble boundary and the area adjacent to the three junction points, the maximum electric field strength parameter of the first state is found to be 18 kV / mm, and the maximum electric field strength parameter of the second state is found to be 27 kV / mm. Based on this, the rate of change of the maximum electric field strength parameter is 0.50.

[0045] Step S15: Normalize and weight the change rate of partial discharge parameters, the change amount of bubble defect parameters, and the change rate of electric field strength parameters to obtain the degradation index of the cement-solid interface and determine the corresponding degradation level.

[0046] It should be noted that, in this embodiment, normalization refers to mapping the rate of change of partial discharge parameters, bubble defect parameters, and electric field strength parameters with different dimensions, orders of magnitude, and value ranges to a unified numerical range; weighted fusion refers to multiplying each normalized parameter by its corresponding weight coefficient and then summing the results; the weight coefficient is a non-negative coefficient characterizing the contribution of each parameter to the degradation of the cement-solid interface, and the sum of all weight coefficients is 1; the degradation index is a dimensionless value that comprehensively reflects the discharge triggering threshold, discharge intensity, discharge frequency, bubble morphology evolution, and the degree of local electric field enhancement; the degradation level refers to the state category determined according to the interval relationship between the degradation index and multiple preset thresholds. The degradation levels are divided into first level, second level, third level, and fourth level according to the degree of degradation from low to high, and are classified according to the first threshold, second threshold, and third threshold. Normalization and weighted fusion can avoid the influence of single parameters on the results by random noise or measurement scale, and improve the reliability of the evaluation through mutual verification between electrical observation, morphological observation, and physical field calculation.

[0047] In one possible implementation, linear normalization based on the minimum and maximum values ​​of historical samples is used, and weighting coefficients are set according to expert experience; in another possible implementation, quantile normalization is used, and weighting coefficients are determined based on the statistical correlation of labeled failed samples.

[0048] For example, in one specific implementation, the normalized partial discharge initiation voltage drop rate, the normalized maximum discharge amplitude growth rate, the normalized discharge number growth rate, the normalized bubble defect parameter change, and the normalized maximum electric field strength parameter change rate are denoted as X1, X2, X3, X4, and X5, respectively, and are calculated according to D=w1 X1+w2 X2+w3 X3+w4 X4+w5 X5 calculates the degradation index D. Taking X1=0.30, X2=0.625, X3=0.70, X4=0.56, X5=0.50, and taking the first weighting coefficient w1=0.25, the second weighting coefficient w2=0.20, the third weighting coefficient w3=0.15, the fourth weighting coefficient w4=0.20, and the fifth weighting coefficient w5=0.20, the degradation index D=0.517 is obtained. Setting the first threshold, second threshold, and third threshold to 0.25, 0.50, and 0.75 respectively, the cement-solid interface is determined to be at level three.

[0049] The following describes the sub-process for determining the degradation level.

[0050] Figure 3 Steps S51 to S54 are used to determine the degradation level in step S15. The first threshold, the second threshold, and the third threshold are set sequentially from low to high according to the degree of degradation, and the first threshold is less than the second threshold, and the second threshold is less than the third threshold.

[0051] Step S51: When the degradation index is less than the first threshold, it is determined to be the first level.

[0052] It should be noted that, in this embodiment, the first threshold refers to the lowest judgment boundary for distinguishing between a stable interface state and an identifiable early degradation state; the first level refers to the interface stability level where the rate of change of partial discharge parameters, the amount of change of bubble defect parameters, and the rate of change of electric field strength parameters are all within the allowable fluctuation range; the allowable fluctuation range refers to the parameter change interval determined based on repeated measurement error, the discreteness of the same batch of test samples, and sensor noise. Determining a degradation index below the first threshold as the first level can avoid misjudging measurement noise or manufacturing discreteness as temperature cycle-induced degradation. In one possible implementation, the first threshold is determined by the high quantile of the degradation index distribution of the same batch of unaged test samples; in another possible implementation, the first threshold is determined by the sum of the upper limit of the degradation index of historically operating samples and the safety margin.

[0053] For example, in one specific implementation, the first threshold is set to 0.25, the degradation index of a certain test sample is 0.18, the computing device determines the test sample as the first level, and outputs the status information "the interface is stable and can continue to be monitored according to the predetermined cycle".

[0054] Step S52: When the degradation index is greater than or equal to the first threshold and less than the second threshold, it is determined to be the second level.

[0055] It should be noted that, in this embodiment, the second threshold refers to the judgment boundary distinguishing between early defect states and obvious defect expansion states; the second level refers to an early defect level where at least one evaluation dimension shows continuous change but has not yet formed a significant multi-dimensional synergistic degradation; continuous change refers to the same parameter continuously changing in the degradation direction at adjacent temperature cycle nodes; significant multi-dimensional synergistic degradation refers to at least two dimensions among partial discharge parameters, bubble defect parameters, and electric field strength parameters simultaneously exceeding their respective warning limits. Determining the test sample whose degradation index is between the first and second thresholds as the second level can prompt for enhanced detection before breakdown or obvious failure. In one possible implementation, the detection interval between subsequent temperature cycle nodes is shortened for the second-level test sample; in another possible implementation, repeated measurements under the same conditions are added to the second-level test sample to eliminate transient interference.

[0056] For example, in one specific implementation, the first threshold and the second threshold are set to 0.25 and 0.50, respectively. The degradation index of a certain test sample is 0.37. The computing device determines the test sample as the second level and shortens the acquisition interval of the next interface image and partial discharge signal from 100 temperature cycles to 50 temperature cycles.

[0057] Step S53: When the degradation index is greater than or equal to the second threshold and less than the third threshold, it is determined to be the third level.

[0058] It should be noted that, in this embodiment, the third threshold refers to the boundary between a defect expansion state that can continue to be controlled for testing and a state requiring high-risk warning; the third level refers to a defect expansion level where the size, number, or connectivity of bubble defects has significantly increased, accompanied by enhanced partial discharge activity or intensified electric field distortion; defect expansion refers to a reproducible increase in the bubble defect region relative to the first state in terms of area, equivalent diameter, or connecting channels. Defining test samples with degradation indices between the second and third thresholds as third-level samples is beneficial for identifying the stage at which the cement-solid interface develops from early discrete bubbles to connected air gaps and concentrated partial discharge regions. In one possible implementation, higher-resolution interface imaging and local mesh refinement model solving are performed on third-level test samples; in another possible implementation, the voltage ramp-up limit for subsequent voltage tests is reduced and the monitoring frequency is increased.

[0059] For example, in one specific implementation, the second threshold and the third threshold are set to 0.50 and 0.75, respectively. The degradation index of a certain test sample is 0.517, and the proportion of bubble area in the second state is significantly increased compared with the first state. The computing device determines the test sample to be of the third level and outputs the status information "defect expansion, it is recommended to review the weak insulation area of ​​the interface".

[0060] Step S54: When the degradation index is greater than or equal to the third threshold, it is determined to be the fourth level.

[0061] It should be noted that, in this embodiment, the fourth level refers to the warning level when partial discharge degradation, bubble defect propagation, and electric field enhancement reach a high-risk range; the high-risk range refers to the unacceptable degradation interval determined based on historical breakdown samples, design insulation margin, or accelerated aging tests; the warning information includes the test sample identifier, degradation index, out-of-limit parameters, location of weak areas in the interface insulation, and recommended handling methods. Determining the degradation index reaching the third threshold as the fourth level can trigger risk control before continued application of high voltage or temperature cycling may cause irreversible insulation damage. In one possible implementation, the fourth level triggers the cessation of pressurization, cessation of temperature cycling, and preservation of original data; in another possible implementation, when the comprehensive degradation index has not yet reached the third threshold but at least two of the following exceed their respective high-risk thresholds: partial discharge initiation voltage drop rate, discharge frequency growth rate, bubble area ratio, and maximum electric field strength parameter change rate: the degradation level is upgraded to the fourth level.

[0062] For example, in one specific implementation, the third threshold is set to 0.75, the degradation index of a certain test sample is 0.82, the computing device determines the test sample to be of the fourth level, stops the square wave voltage source output and saves the partial discharge signal, interface image, electric field calculation results and alarm time.

[0063] Step S16: Determine the equivalent stress field of the cement-solid interface in the second state and extract the stress peak region. Based on the spatial overlap between the stress peak region and the bubble defect region, determine the weak insulation region of the interface.

[0064] It should be noted that, in the embodiments of this application, the equivalent stress field refers to the spatial distribution formed after converting the multiaxial stress caused by the temperature field and the mismatch of material thermal expansion into the von Mises equivalent stress corresponding to each model mesh position; the stress peak region refers to the continuous model mesh region in the equivalent stress field that is not less than the preset stress quantile value or the preset stress threshold; the preset stress quantile value refers to the value located at the predetermined percentile after arranging the equivalent stress of all model meshes from small to large; the spatial overlap refers to the ratio obtained by dividing the intersection area of ​​the stress peak region and the bubble defect region after coordinate registration by the union area of ​​the two; coordinate registration refers to establishing the translation, rotation, scaling or perspective transformation relationship between the interface image coordinates and the model coordinates using electrode edges, substrate corners or preset marker points; the interface insulation weak region refers to the region determined by the intersection of the stress peak region and the bubble defect region when the spatial overlap reaches the preset threshold.

[0065] Spatially matching the stress concentration locations predicted by the model with the measured locations of bubble defects can link temperature cycling causes, bubble morphology results, and insulation risk locations. In one possible implementation, the stress peak region is extracted using the 95th percentile of the equivalent stress field, and the spatial overlap threshold is set to 0.30; in another possible implementation, the preset stress threshold and spatial overlap threshold are reverse-calibrated based on failure samples from the same batch.

[0066] For example, in one specific implementation, the temperature cycling boundary condition corresponding to the second state is applied to the thermo-mechanical coupling model, and the model mesh at or above the 95th percentile in the equivalent stress field is extracted as the stress peak region. After coordinate registration using three corresponding marker points on the edge of the copper electrode, the intersection area of ​​the stress peak region and the bubble defect region is 0.021 mm², the union area is 0.050 mm², and the spatial overlap is 0.42, which is higher than the preset threshold of 0.30. Therefore, the 0.021 mm² intersection region is determined as the weak interface insulation region, and its contour is marked on the output interface image. Here, the thermo-mechanical coupling model refers to a numerical model that takes the geometry of the test sample, the thermodynamic parameters of the material, and the preset temperature cycling boundary condition as inputs, and solves the temperature field, displacement field, and stress field sequentially or jointly. The thermodynamic parameters of the material include thermal conductivity, specific heat capacity, density, elastic modulus, Poisson's ratio, and coefficient of thermal expansion.

[0067] Example 2; See Figure 5 This application provides a partial discharge degradation assessment system for bubble defects at the cement interface of a high-voltage power module. For example... Figure 5 As shown, the system includes a temperature cycling assembly 1, a sample clamp 2, a square wave voltage source 3, a partial discharge sensor 4, an image acquisition unit 5, and a computing device 6. The temperature cycling assembly 1 applies a preset temperature cycle to the sample to be tested; the sample clamp 2 is used to hold the sample in a repeatable position; the output of the square wave voltage source 3 is connected to the electrode of the sample to be tested mounted on the sample clamp; the partial discharge sensor 4 is positioned opposite the cemented interface of the sample to be tested; the optical axis of the image acquisition unit 6 faces the cemented interface; the outputs of both the partial discharge sensor 4 and the image acquisition unit 5 are connected to the computing device 6. The computing device 6 includes a processor, a memory, a signal acquisition interface, and an image acquisition interface. When the program stored in the memory is executed by the processor, the system performs the partial discharge degradation assessment of the cemented interface bubble defects of the high-voltage power module provided in Example 1 to complete the degradation assessment.

[0068] In this embodiment, the temperature cycling assembly refers to an environmental loading device comprising a programmable temperature-controlled chamber, a heating unit, a cooling unit, a temperature sensor, and a controller; the programmable temperature-controlled chamber refers to a sealed space for accommodating the test sample and changing its internal temperature according to a preset temperature curve; the sample clamp refers to a mechanical positioning structure for fixing the test sample, and the sample clamp includes an insulating support, an electrode connector, and a position reference component; the position reference component refers to a limiting structure or marking structure for restoring the test sample to the same clamping position at different acquisition times. The cooperation between the temperature cycling assembly and the sample clamp ensures that the thermal load path and the position of the test sample are consistent, providing conditions for subsequent pairing and comparison of partial discharge signals and interface images.

[0069] In this embodiment, the square wave voltage source refers to a power supply capable of outputting periodic high and low levels and adjusting the frequency, pulse width, voltage amplitude, rise time, and fall time; the rise time and fall time are used to characterize the rate of change of the square wave voltage; the partial discharge sensor refers to a detection device that converts the high-frequency electromagnetic components generated by partial discharge at the cement-solid interface into electrical signals; the image acquisition unit includes an imaging lens, an image sensor, an illumination unit, and a scale calibration unit; the optical axis refers to the central propagation direction of the imaging optical system; the signal acquisition interface refers to the interface for sampling, quantizing, and time-stamping the output of the partial discharge sensor; the image acquisition interface refers to the interface for receiving interface images and saving the acquisition time, magnification, and calibration ratio. By sharing a trigger clock or timestamp to associate the partial discharge signal and the interface image, electrical changes and morphological changes can be correlated to the same test sample and the same temperature cycle node.

[0070] In this application embodiment, a computing device refers to an electronic device having a processor, a memory, and a data interface and capable of executing a preset program; a processor refers to an arithmetic unit that executes signal processing instructions and numerical operations; and a memory refers to a storage medium that stores raw data, programs, parameters, and calculation results.

[0071] The above system can be implemented as an integrated device, or it can be implemented by combining temperature cycling equipment, partial discharge testing equipment, imaging equipment and computing equipment through a data interface.

[0072] For specific details and benefits of the partial discharge degradation assessment device for bubble defects at the cement interface of high-voltage power modules provided in the embodiments of this application, please refer to the above description of the partial discharge degradation assessment method for bubble defects at the cement interface of high-voltage power modules, which will not be repeated here.

[0073] It should be noted that the terms "first," "second," and similar terms used in this application do not indicate any order, quantity, or importance, but are merely used to distinguish different parts. Terms such as "including" or "comprising" mean that the element preceding the word covers the element listed after the word, and do not exclude the possibility of covering other elements as well.

[0074] Although the operations are described in a specific order in the accompanying drawings in this application, it should not be construed as requiring these operations to be performed in the specific order or serial order shown, or requiring all of the shown operations to obtain the desired result. In certain environments, multitasking and parallel processing may be advantageous.

[0075] Finally, it should be noted that the above content is only used to illustrate the technical solution of this application, and is not intended to limit the scope of protection of this application. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of this application shall not depart from the substance and scope of the technical solution of this application.

Claims

1. A method for evaluating the partial discharge degradation of bubble defects at the cement interface of a high-voltage power module, characterized in that, include: Acquire the partial discharge signal and interface image of the cement-solid interface of the test sample in the first and second states. The first state is the state in which no preset temperature cycle has been applied, and the second state is the state in which the preset temperature cycle has been applied; Based on the partial discharge signal, partial discharge parameters are extracted, and the rate of change of partial discharge parameters in the second state relative to the first state is determined using the partial discharge parameters in the first state as a reference. The bubble defect region is segmented from the interface image and the bubble defect parameters are extracted. Based on the bubble defect parameters in the first state, the change in bubble defect parameters in the second state relative to the first state is determined. An electric field model containing the bubble defect region is established and the electric field strength parameters are solved. Using the electric field strength parameters of the first state as a reference, the rate of change of the electric field strength parameters of the second state relative to the first state is determined. The rate of change of the partial discharge parameter, the amount of change of the bubble defect parameter, and the rate of change of the electric field strength parameter are normalized and weighted to obtain the degradation index of the cement-solid interface and determine the corresponding degradation level.

2. The method for evaluating partial discharge degradation of bubble defects at the cement interface of high-voltage power modules according to claim 1, characterized in that, The test sample includes an electrode, a silicone gel encapsulation layer, and a ceramic substrate. The electrode, the silicone gel encapsulation layer, and the ceramic substrate intersect on the test sample to form a three-way bonding point. The gel-ceramic interface includes a silicone gel-ceramic interface and a silicone gel-electrode interface located in the adjacent region of the three-way bonding point.

3. The method for evaluating partial discharge degradation of bubble defects at the cement interface of high-voltage power modules according to claim 1, characterized in that, Also includes: The equivalent stress field of the cement-bonded interface in the second state is determined and the stress peak region is extracted. Based on the spatial overlap between the stress peak region and the bubble defect region, the weak insulation region of the interface is determined.

4. The method for evaluating partial discharge degradation of bubble defects at the cement interface of high-voltage power modules according to claim 3, characterized in that, The stress peak region is composed of a grid region in the equivalent stress field that is not less than a preset stress quantile value; the spatial overlap includes the ratio of the area of ​​the intersection region of the stress peak region and the bubble defect region to the area of ​​the union region of the stress peak region and the bubble defect region; When the spatial overlap is greater than or equal to a preset threshold, the intersection area of ​​the stress peak area and the bubble defect area is determined as the weak interface insulation area.

5. The method for evaluating partial discharge degradation of bubble defects at the cement interface of high-voltage power modules according to claim 1, characterized in that, The partial discharge parameters include the partial discharge initiation voltage, the maximum discharge amplitude, and the number of discharges; the bubble defect parameters include the number of bubbles, the average equivalent diameter, the maximum equivalent diameter, the bubble area ratio, and the bubble connectivity; the electric field strength parameters include the maximum electric field strength parameters of the bubble defect region.

6. The method for evaluating partial discharge degradation of bubble defects at the cement interface of high-voltage power modules according to claim 5, characterized in that, The partial discharge parameter change rate includes the partial discharge initiation voltage decrease rate, the maximum discharge amplitude growth rate, and the discharge number growth rate; the bubble defect parameter change is the fusion result obtained by normalizing and weighting the parameter change corresponding to at least two bubble defect parameters; the electric field strength parameter change rate includes the maximum electric field strength parameter change rate of the bubble defect region.

7. The method for evaluating partial discharge degradation of bubble defects at the cement interface of high-voltage power modules according to claim 6, characterized in that, The formula for calculating the degradation index includes: D=w1 X1+w2 X2+w3 X3+w4 X4+w5 X5; Where D is the degradation index, X1 is the normalized partial discharge initiation voltage decrease rate, X2 is the normalized maximum discharge amplitude growth rate, X3 is the normalized discharge number growth rate, X4 is the normalized bubble defect parameter change, X5 is the normalized maximum electric field strength parameter change rate, w1 is the first weighting coefficient, w2 is the second weighting coefficient, w3 is the third weighting coefficient, w4 is the third weighting coefficient, w5 is the fifth weighting coefficient, and w1+w2+w3+w4+w5=1.

8. The method for evaluating partial discharge degradation of bubble defects at the cement interface of high-voltage power modules according to claim 1, characterized in that, The preset temperature cycle includes a low temperature section, a high temperature section, a heating section, a cooling section, and at least one constant temperature holding section; the temperature of the low temperature section is between -40℃ and 0℃, the temperature of the high temperature section is between 125℃ and 175℃, the absolute value of the temperature change rate of the heating section and the cooling section is between 0.1℃ / min and 15℃ / min, and the holding time of the constant temperature holding section is between 5min and 30min.

9. The method for evaluating partial discharge degradation of bubble defects at the cement interface of high-voltage power modules according to claim 1, characterized in that, The degradation levels are classified into four levels, from lowest to highest, according to the degree of degradation: Level 1, Level 2, Level 3, and Level 4. When the degradation index is less than the first threshold, it is determined to be the first level; When the degradation index is greater than or equal to the first threshold and less than the second threshold, it is determined to be the second level; When the degradation index is greater than or equal to the second threshold and less than the third threshold, it is determined to be the third level; When the degradation index is greater than or equal to the third threshold, it is determined to be the fourth level; Wherein, the first threshold is greater than the second threshold, and the second threshold is greater than the third threshold.

10. A partial discharge degradation assessment system for bubble defects at the cement interface of a high-voltage power module, characterized in that, It includes a temperature cycling assembly, a sample holder, a square wave voltage source, a partial discharge sensor, an image acquisition unit, and a computing device; The temperature cycling assembly is used to apply a preset temperature cycle to the test sample; the sample clamp is used to clamp the test sample; the output terminal of the square wave voltage source is connected to the electrode of the test sample mounted on the sample clamp; the partial discharge sensor is positioned opposite to the adhesive interface of the test sample; the optical axis of the image acquisition device is oriented towards the adhesive interface; the output terminals of the partial discharge sensor and the image acquisition device are both connected to the computing device. The computing device is configured to perform the partial discharge degradation assessment method for bubble defects at the cement interface of a high-voltage power module as described in any one of claims 1-9.

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