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At present, the current-fed full-bridge DC-DC converter still faces two inherent defects, namely, the soft-start issue during the start-up process and the voltage spike issue in normal working conditions. In existing research, a large number of attempts have been reported to overcome these two inherent issues. However, the existing solutions are all based on both redundant soft-start circuits and snubber circuits, and two different circuits are required. As a result, the cost of the current-fed full-bridge DC-DC converter is high, especially because the soft-start circuits are only used during the start-up process. So, to reduce device redundancy, a hardware-simplified soft-start scheme is proposed in this paper. In the proposed scheme, the snubber circuit is reused for the soft-start process based on topology reconfiguration, avoiding additional soft-start circuits to reduce the cost of this DC-DC converter. In this proposed method, the current-fed full-bridge DC-DC converter is operated as the voltage-fed full-bridge DC-DC converter by always turning on the snubber switch during the start-up process. Then, the output capacitor can be charged by slowly increasing the output voltage of the H bridge. Then, when the output voltage is high enough, the current-fed full-bridge DC-DC converter is again operated in the current-fed mode to boost the voltage. Subsequently, the converter characters and control strategy were examined and analyzed. The experimental results verify the feasibility of the proposed hardware-simplified soft-start scheme for the current-fed full-bridge DC-DC converter. [ABSTRACT FROM AUTHOR]

Low crystalline photocatalysts with unsaturated active sites, such as oxygen vacancy (Ov), is reported to exhibit enhanced adsorption and activation of oxygen‐containing small molecules, such as H2O and CO2, thus boosting the activity in photocatalytic H2 evolution and CO2 reduction. However, numerous low‐crystalline photocatalysts show unsatisfactory stability due to the easily repaired surface Ov. Herein, three SnNb2O6 with different crystallinity were prepared by hydrothermal approach with similar precursors. Compared with bulk SnNb2O6 and ultra‐thin layered SnNb2O6, low‐crystalline SnNb2O6 (SNA) exhibits optimal visible‐light‐driven evolution rates of H2 (86.04 μmol g−1 h−1) and CO from CO2 (71.97 μmol g−1 h−1), which is mainly ascribed to the fast separation of the photogenerated carriers and enhanced photoreduction power caused by the surface Ov. More importantly, the sharp decrease of photocatalytic activity of SNA after seven cycles is well restored by the hydrothermal treatment of recycled SNA, ascribed to the reactivated surface Ov with the recovered low‐crystalline structure. These works thus offer a promising strategy for developing low‐crystalline and amorphous photocatalysts with high activity and stability. [ABSTRACT FROM AUTHOR]

A simple detection and ride-through operation approach is proposed for star-connected cascaded H-bridge (CHB) converter-based STATCOMs with a single IGBT open circuit fault. It adopts a modified current regulator with high gains at both dc and fundamental frequencies. Then, the output signals of the current regulator branches and the dc voltage balancing regulator are synthesized as an inherent indicator to quickly determine the position of the open-circuit fault IGBT. With this approach, the controller can also be considered as an inherent system state monitor, but without any additional sensors or computing burdens. Afterwards, in the ride-through operation stage, the faulty H-bridge module can switch to half-bridge operation and the corresponding dc offset voltage is compensated by the remaining healthy modules. It has been validated that the proposed approach is accurate in various conditions, including grid voltage and load disturbances. [ABSTRACT FROM AUTHOR]

Pollutants in the atmosphere have been linked to poor pregnancy outcomes in women. However, such investigations are scarce in metropolitan northern China. The major exposure window of air pollution affecting pregnant women is also unknown. For the analysis, this retrospective cohort study enrolled 6960 pregnant women recorded at Tongchuan People's Hospital from January 2018 to December 2019. Pollutant concentration values from the nearest monitoring station to the pregnant women were used to estimate exposure doses for each exposure window. Logistic regression models were created to investigate the connection between pollutants and spontaneous abortion while controlling for confounding factors. PM2.5 was a risk factor for spontaneous abortion in T3 (30–60 days before the first day of the last menstrual period [LMP]), (OR: 1.305, 95% CI: 1.143–1.490) and T4 (60–90 days before the first day of the LMP),(OR: 1.450, 95% CI: 1.239–1.696) after controlling for covariates. In the same window, PM10 was a risk factor (OR: 1.308, 95% CI: 1.140–1.500), (OR: 1.386, 95% CI: 1.184–1.621). In T2 (30 days before the first day of the LMP), T3, and T4, SO2 was a risk factor for spontaneous abortion (OR: 1.185, 95% CI: 1.025–1.371), (OR: 1.219, 95% CI: 1.071–1.396), (OR: 1.202, 95% CI: 1.040–1.389). In T3 and T4, NO2 was a risk factor (OR: 1.171, 95% CI: 1.019– 1.346), (OR: 1.443, 95% CI: 1.259–1.655). In T1 (from the first day of the LMP to the date of abortion), O3 was found to be a risk factor (OR: 1.366, 95% CI: 1.226–1.521). Exposure to high levels of air pollutants before and during pregnancy may be a risk factor for spontaneous abortion in pregnant women. This study further illustrates the importance of reducing air pollution emissions. [ABSTRACT FROM AUTHOR]