Mechanical stress is a crucial factor affecting the life and insulation performance of DC-link capacitors (DCLCs). However, at present, there is a lack of long-term experimental observations on the effects of mechanical stress on the life and insulation performance of DCLCs. The element-winding process for DCLCs is carried out by winding metalized film on a reel and adjusting the various winding tensions and pressures according to performance requirements, usually with a winding tension coefficient (WTC) of k_T = 1.5. The pull pressure of the winding machine on the film produces tension during the elements’ winding process, and the tension in the film grows after the heat-setting process. In this study, by adjusting the four tension coefficients of the elements in the winding process, which were 1.4, 1.5, 1.6, and 1.7, various winding tensions of the DCLC components were changed. Additionally, various heat-setting shrinkage tensions were appropriately generated by setting different heat-setting temperatures (HSTs). Relevant test platforms were established, and a life aging test, insulation resistance measurement, and withstand voltage test were performed on these DCLCs at different tension coefficients and HSTs. The obtained results reveal that the mechanical stress of DCLCs is affected by the parameters of the material itself, including the tension coefficient during the winding process and the HST. The winding tension affects the life of DCLCs, such that those with the highest tension (k_T = 1.7) demonstrate the longest life at an HST of 105 °C, whereas samples with the lowest tension (k_T = 1.4) exhibit the longest life at an HST of 110 °C. HSTs are capable of improving the lifetime of DCLCs. HSTs are also able to improve the withstand voltage capability of DCLCs, but the tension is not proportional to the withstand voltage capability of DCLCs. This research provides a suitable basis for further explorations of the life and insulation performance of DCLCs.

A 3D Electrical Impedance Tomography (EIT) method based on Dimensional Grey Wolf Optimization (DGWO) algorithm is proposed for reconstructing 3D images of breast tumors, overcomes the inherent defects of 3D EIT with high shape sensitivity and position sensitivity. In this study, a combination of multiple ellipsoids is used to mimic the shape of a breast tumor. The EIT problem is transformed into an optimization problem, which is solved by constructing an objective function and employing a sensitivity matrix approach. Finally, the optimization problem is solved using DGWO algorithm. In the simulation, a 16-electrode tapered sensor is used to randomly generate a tumor model and compared with the Tikhonov regularization algorithm and the combination of Tikhonov and NOSER regularization algorithm (TK-NOSER) to validate the performance of the proposed algorithm. Simulation results show that the DGWO algorithm differs little from the traditional regularization algorithm when the target is located in the center, while the advantage of the DGWO algorithm is more obvious when the target is located at the edge and non-spherical. DGWO algorithm improves the image correlation coefficient (IC) and image error (IE) by 12.20% and 24.00%, respectively, when the target is at the edge position. In the experiment, water and agar models of specific conductivity were used to simulate mammary glands and tumors. The experimental results show that the DGWO algorithm is superior to the TK-NOSER algorithm in terms of imaging accuracy and imaging artifacts, in which the average IC and average IE of the DGWO algorithm are improved by 19.14% and 15.12%, respectively. Therefore, the constructed experimental platform and the proposed algorithm achieve accurate imaging of target size and shape, which is expected to be applied to the clinical detection of breast cancer.

Insulation resistance is a vital factor in dry DC link capacitors (DCLCs), and crucially influences their voltage equalization and energy storage performance. However, at present, there is a lack of experimental observation on the insulation resistance characteristics of DCLCs in the presence of high temperatures and operating voltages. In the present study, the insulation resistance and conductivity of DCLCs are methodically analyzed. For this purpose, the corresponding test platform is appropriately fabricated, the insulation resistance measurement experiments are performed at various temperatures and operating voltages, and the factors affecting the insulation resistance and conductivity of the DCLC are carefully examined. The results reveal that the insulation resistance of the DCLC reduces exponentially with the growth in voltage and operating temperature. When the operating voltage becomes greater than 4480 V or the operating temperature reaches higher than 70 °C, the decline in insulation resistance slows down. The conductivity of metalized polypropylene film in the DCLC increases exponentially with increasing voltage and temperature. By increasing the operating voltage from 1960 V to 5600 V and the temperature from 20 °C to 90 °C, the DCLC’s insulation resistance exhibits a descending trend from 891.30 MΩ to 2.14 MΩ, while its conductivity grows from 3.49 × 10⁻¹⁶ S/m to 1.47 × 10⁻¹³ S/m. The results reveal that the key factors affecting the insulation resistance of the DCLC are the polypropylene film and the metal evaporated from the metal layer. This research is anticipated to provide a valuable reference for the further development of science and technology pertinent to the insulation resistance of DCLCs.

DC link capacitors (DCLCs) are key devices in converters. The relative humidity affects the performance of the elements of a DCLC. Currently, there are relatively few studies on the effect of relative humidity on the electrical characteristics of the elements of DCLCs during the production process. This study describes the effects and the control of the relative humidity in the production process. For this purpose, a DCLC component withstand voltage test platform and a DCLC component aging test platform were established. The voltage withstand tests were conducted during different processes and at different relative humidities, and life aging tests were conducted at different relative humidities and different storage times. The results show that after the winding and metal-spraying processes, the voltage withstand levels of the components stored at 30% RH, 60% RH, and 80% RH were very close to that of the components at 3000 VDC; after the heat-setting process, the voltage withstand levels of the components stored at 30% RH, 60% RH, and 80% RH showed a decreasing tendency compared with the level of the components at 3000 VDC. Regarding the samples, after the heat-setting process, stored at 30% RH and 60% RH for 24 h, 96 h, 168 h, 240 h, and 336 h and 2000 h of the aging tests, the capacitance decreases monotonically as the storage time is increased but never exceeds 3%, and the capacitance change decreases as the relative humidity increases. This study can provide important guidance for the humidity control of various processes in the production of DCLCs.

Thermal stress is an important factor affecting the life of a DC link capacitor (DCLC). However, relevant studies on thermal stress mechanism directly influencing the lifetime of the capacitor are rarely reported. In this paper, the heat setting and thermal stress of DCLC has been analyzed, and the relevant experimental platforms have been developed to evaluate the breakdown strength of DCLC at two heat setting temperatures (HSTs). Simultaneously, the life aging analysis of DCLC at different HSTs and the life aging tests at various temperatures were also executed to attain insights into the influence of thermal stress on the lifetime of DCLC. The results showed that the stress caused by heat setting and operating temperature influenced the breakdown voltage capability and the lifetime of DCLC. With an increase in HST by 5 °C, a step-increase in the withstand voltage capability of DCLC from 7,000 V to 7,200 V was observed that demonstrated an enhancement of 2.86% in the breakdown strength performance. Correspondingly, the lifetime of DCLC with a capacitance change rate of -3% enhanced from 1,500 h to 1,700 h. However, severe deterioration in the life span of DCLC from 4,200 h to 500 h was observed with an increasing operating temperature from 55 °C to 85 °C, respectively. The lifetime could be enhanced by increasing the HST as well as reducing the operating temperature. The presented results could be termed a harbinger for industrial production of high-performance DCLC with enhanced lifetime that augers well for high-power applications.

Thermal stress is an important factor affecting the life of a DC link capacitor (DCLC). However, relevant studies on thermal stress mechanism directly influencing the lifetime of the capacitor are rarely reported. In this paper, the thermal polymerization of DCLC has been analyzed, and the relevant experimental platforms have been developed to evaluate the breakdown strength of DCLC at two thermal polymerization temperatures (TPTs). Simultaneously, the aging analysis of DCLC at different TPTs and the accelerated lifetime measurements at various temperatures were also executed to attain insights into the influence of thermal stress on the lifetime of DCLC. The results showed that the stress caused by thermal polymerization and working temperature influenced the breakdown voltage capability and the lifetime of DCLC. With an increase in TPT by 5 °C, a step-increase in the withstand voltage capability of DCLC from 7,000 V to 7,200 V was observed that demonstrated an enhancement of 2.86%in the breakdown strength performance. Correspondingly, the lifetime of DCLC with a capacitance change rate of -3% enhanced from 1,500 hours to 1,700 hours. However, severe deterioration in the life span of DCLC from 4,200 hours to 500 hours was observed with an increasing operating temperature from 55 °C to 85 °C, respectively. The lifetime could be enhanced by increasing the thermal polymerization temperature as well as reducing the working temperature. The presented results could be termed a harbinger for industrial production of high-performance DCLC with enhanced lifetime that augers well for high-power applications.