Optimized Low-Switching-Loss PWM and Neutral-Point Balance Control Strategy of Three-Level NPC Inverters

Shi-Zhou Xu,Chun-Jie Wang,Tian-Cheng Han,Xue-Ping Li,Xiang-Yu Zhu 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.3

Power loss reduction and total harmonic distortion(THD) minimization are two important goals of improving three-level inverters. In this paper, an optimized pulse width modulation (PWM) strategy that can reduce switching losses and balance the neutral point with an optional THD of three-level neutral-point-clamped inverters is proposed. An analysis of the two-level discontinuous PWM (DPWM) strategy indicates that the optimal goal of the proposed PWM strategy is to reduce switching losses to a minimum without increasing the THD compared to that of traditional SVPWMs. Thus, the analysis of the two-level DPWM strategy is introduced. Through the rational allocation of the zero vector, only two-phase switching devices are active in each sector, and their switching losses can be reduced by one-third compared with those of traditional PWM strategies. A detailed analysis of the impact of small vectors, which correspond to different zero vectors, on the neutral-point potential is conducted, and a hysteresis control method is proposed to balance the neutral point. This method is simple, does not judge the direction of midpoint currents, and can adjust the switching times of devices and the fluctuation of the neutral-point potential by changing the hysteresis loop width. Simulation and experimental results prove the effectiveness and feasibility of the proposed strategy.

Effect of synthesis conditions on the particle size and morphology of YAG powder

Jie-Guang Song,Fang Wang,Ming-Han Xu,Yin-Yan Ju,Yang-Liang Li,Shi-Bin Li,Gang-Chang Ji 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.2

Yttrium aluminum garnet (YAG) is currently a widely applied structural and functional material. To prepare highperformance YAG ceramics we prepared pure YAG powder, after calcining the precursor at 1100 ºC, by co-precipitation with ammonia as the precipitant and aluminum nitrate as well as yttrium nitrate as raw materials. The preparation conditions for the YAG precursor were a pH of 9, a titration rate of 10 ml/ minute and a reaction time of 60 minutes. The mean paricle size of the YAG powder was 11ìm. The mean particle size for the YAG powder increased with an increase in the pH and at a higher pH the YAG particles were more irregular in shape. The mean particle size and particle size distribution range of the YAG powder increased with an increase in the titration rate. For the YAG powder with a higher mean particle size, the particle size distribution range was wider but the size of most YAG particles was still small and the YAG particles were nearly spherical.

The effect of the oxidation conditions on the surface microdomains of ZrB2-YAG ultra-high temperature ceramics

Jie-Guang Song,Min-Han Xu,Da-Ming Du,Fang Wang,Shi-Bin Li,Gang-Chang Ji 한양대학교 세라믹연구소 2013 Journal of Ceramic Processing Research Vol.14 No.4

Zirconium diboride is widely applied because of some excellent properties. The effect of the oxidation temperature on the surface microdomain of ZrB2-YAG multi-phase ceramics was studied, it helps to improve the performance of ultra-hightemperature ceramics. The results show the oxidation layer thickness is increased with an increase in the oxidation temperature, the oxidation layer thickness is decreased by increasing the density of multi-phase ceramics at the same oxidation temperature. The ceramic surface shows the (m)ZrO2, YAG, B2O3 and ZrB2 phases below the the oxidation temperature at 1300 ο C, but the ceramic surface do not show the ZrB2 phase above the oxidation temperature at 1300 ο C that is to say, the ZrB2 phase of the ceramic suface is entirely oxidized. The oxidation layer thickness is increased with an increase in the oxidation time, however, the ratio of increasing thickness is less and less. The oxidation layer shows a loose structure during the initial stage of the oxidation, which lacks a barriers for the diffusion of the oxygen.

The effect of a reinforcement phase on the oxidation mechanism of ZrB2-YAG-Al2O3 ceramcis

Jie-Guang Song,Fang Wang,Ming-Han Xu,Shi-Bin Li,Gang-Chang Ji 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.3

ZrB2 and YAG are widely applied because of some excellent properties, but ZrB2 is easily oxidized in high-temperature air. To make ZrB2 ceramics have a better oxidation resistance, high-density ZrB2-YAG-Al2O3 ceramics were prepared. The effect of a reinforcement phase on the oxidation mechanism of ZrB2-YAG-Al2O3 ceramics is investigated at different high temperature ranges. The results show that the overall tendency of the weight gain of ZrB2-YAG ceramics and ZrB2 ceramics are similar, but the weight gain of ZrB2-YAG ceramics is less than that of ZrB2 ceramics. The weight gain tendency of three types of ceramics are similar below 1000, the weight gain of ZrB2-YAG and ZrB2-YAG-Al2O3 ceramics have a mild tendency between 1000 and 1300, the weight gain tendency of ZrB2-YAG ceramics and ZrB2 ceramics are similar at 1300, however, the weight gain tendency of ZrB2-YAG-Al2O3 ceramics became mild at 1300 due to the Al18B4O33 coating on the ceramic surface. The weight gain rapidly increased for 1h, then the weight gain tendency became mild after 1 h. The weight gain tendency of ZrB2-YAG-Al2O3 ceramics is similar by contrast with ZrB2-YAG ceramics and ZrB2 ceramics for 1 h, the weight gain tendency of ZrB2-YAG-Al2O3 ceramics is extremely mild at a higher oxidation temperature after 1 h. ZrB2 and YAG are widely applied because of some excellent properties, but ZrB2 is easily oxidized in high-temperature air. To make ZrB2 ceramics have a better oxidation resistance, high-density ZrB2-YAG-Al2O3 ceramics were prepared. The effect of a reinforcement phase on the oxidation mechanism of ZrB2-YAG-Al2O3 ceramics is investigated at different high temperature ranges. The results show that the overall tendency of the weight gain of ZrB2-YAG ceramics and ZrB2 ceramics are similar, but the weight gain of ZrB2-YAG ceramics is less than that of ZrB2 ceramics. The weight gain tendency of three types of ceramics are similar below 1000, the weight gain of ZrB2-YAG and ZrB2-YAG-Al2O3 ceramics have a mild tendency between 1000 and 1300, the weight gain tendency of ZrB2-YAG ceramics and ZrB2 ceramics are similar at 1300, however, the weight gain tendency of ZrB2-YAG-Al2O3 ceramics became mild at 1300 due to the Al18B4O33 coating on the ceramic surface. The weight gain rapidly increased for 1h, then the weight gain tendency became mild after 1 h. The weight gain tendency of ZrB2-YAG-Al2O3 ceramics is similar by contrast with ZrB2-YAG ceramics and ZrB2 ceramics for 1 h, the weight gain tendency of ZrB2-YAG-Al2O3 ceramics is extremely mild at a higher oxidation temperature after 1 h.

Diffusion-Weighted Imaging for the Left Hepatic Lobe has Higher Diagnostic Accuracy for Malignant Focal Liver Lesions

Han, Xue,Dong, Yin,Xiu, Jian-Jun,Zhang, Jie,Huang, Zhao-Qin,Cai, Shi-Feng,Yuan, Xian-Shun,Liu, Qing-Wei Asian Pacific Journal of Cancer Prevention 2014 Asian Pacific journal of cancer prevention Vol.15 No.15

Background: This study was conducted to investigate whether apparent diffusion coefficient (ADC) measurements by dividing the liver into left and right hepatic lobes may be utilized to improve the accuracy of differential diagnosis of benign and malignant focal liver lesions. Materials and Methods: A total of 269 consecutive patients with 429 focal liver lesions were examined by 3-T magnetic resonance imaging that included diffusion-weighted imaging. For 58 patients with focal liver lesions of the same etiology in left and right hepatic lobes, ADCs of normal liver parenchyma and focal liver lesions were calculated and compared using the paired t-test. For all 269 patients, ADC cutoffs for focal liver lesions and diagnostic accuracy in the left hepatic lobe, right hepatic lobe and whole liver were evaluated by receiver operating characteristic curve analysis. Results: For the group of 58 patients, mean ADCs of normal liver parenchyma and focal liver lesions in the left hepatic lobe were significantly higher than those in the right hepatic lobe. For differentiating malignant lesions from benign lesions in all patients, the sensitivity and specificity were 92.6% and 92.0% in the left hepatic lobe, 94.4% and 94.4% in the right hepatic lobe, and 90.4% and 94.7% in the whole liver, respectively. The area under the curve of the right hepatic lobe, but not the left hepatic lobe, was higher than that of the whole liver. Conclusions: ADCs of normal liver parenchyma and focal liver lesions in the left hepatic lobe were significantly higher than those in the right hepatic lobe. Optimal ADC cutoff for focal liver lesions in the right hepatic lobe, but not in the left hepatic lobe, had higher diagnostic accuracy compared with that in the whole liver.

Optimized Low-Switching-Loss PWM and Neutral-Point Balance Control Strategy of Three-Level NPC Inverters

Xu, Shi-Zhou,Wang, Chun-Jie,Han, Tian-Cheng,Li, Xue-Ping,Zhu, Xiang-Yu The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.3

Power loss reduction and total harmonic distortion(THD) minimization are two important goals of improving three-level inverters. In this paper, an optimized pulse width modulation (PWM) strategy that can reduce switching losses and balance the neutral point with an optional THD of three-level neutral-point-clamped inverters is proposed. An analysis of the two-level discontinuous PWM (DPWM) strategy indicates that the optimal goal of the proposed PWM strategy is to reduce switching losses to a minimum without increasing the THD compared to that of traditional SVPWMs. Thus, the analysis of the two-level DPWM strategy is introduced. Through the rational allocation of the zero vector, only two-phase switching devices are active in each sector, and their switching losses can be reduced by one-third compared with those of traditional PWM strategies. A detailed analysis of the impact of small vectors, which correspond to different zero vectors, on the neutral-point potential is conducted, and a hysteresis control method is proposed to balance the neutral point. This method is simple, does not judge the direction of midpoint currents, and can adjust the switching times of devices and the fluctuation of the neutral-point potential by changing the hysteresis loop width. Simulation and experimental results prove the effectiveness and feasibility of the proposed strategy.

Effect of Tensile Deformation of Austenite on the Morphology and Strength of Lath Martensite

Zengmin Shi,Kai liu,Maoqiu Wang,Jie Shi,Han Dong,Jian Pu,Bo Chi,Yisheng Zhang,Li Jian 대한금속·재료학회 2012 METALS AND MATERIALS International Vol.18 No.2

A hot-rolled steel, 22SiMn2TiB, was employed to study the effect of austenite deformation on the micro-structure and strength of the subsequently formed lath martensite. It was revealed that the sizes of the mar-tensite packet, block and lath were refined by the tensile deformation of austenite at temperatures above 850 °C. With the increase of the deformation temperature, the packet size increased, whereas the block size decreased. The width of the lath was independent of the prior austenite grain size and the deformation temperature. The refinement of martensite blocks was considered to strengthen the ausformed martensite.

Hydrogen sulfide restores cardioprotective effects of remote ischemic preconditioning in aged rats via HIF-1α/Nrf2 signaling pathway

Wang, Haixia,Shi, Xin,Cheng, Longlong,Han, Jie,Mu, Jianjun The Korean Society of Pharmacology 2021 The Korean Journal of Physiology & Pharmacology Vol.25 No.3

The present study explored the therapeutic potential of hydrogen sulfide (H2S) in restoring aging-induced loss of cardioprotective effect of remote ischemic preconditioning (RIPC) along with the involvement of signaling pathways. The left hind limb was subjected to four short cycles of ischemia and reperfusion (IR) in young and aged male rats to induce RIPC. The hearts were subjected to IR injury on the Langendorff apparatus after 24 h of RIPC. The measurement of lactate dehydrogenase, creatine kinase and cardiac troponin served to assess the myocardial injury. The levels of H2S, cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE), nuclear factor erythroid 2-related factor 2 (Nrf2), and hypoxia-inducible factor (HIF-1α) were also measured. There was a decrease in cardioprotection in RIPC-subjected old rats in comparison to young rats along with a reduction in the myocardial levels of H2S, CBS, CSE, HIF-1α, and nuclear: cytoplasmic Nrf2 ratio. Supplementation with sodium hydrogen sulfide (NaHS, an H2S donor) and l-cysteine (H2S precursor) restored the cardioprotective actions of RIPC in old hearts. It increased the levels of H2S, HIF-1α, and Nrf2 ratio without affecting CBS and CSE. YC-1 (HIF-1α antagonist) abolished the effects of NaHS and l-cysteine in RIPC-subjected old rats by decreasing the Nrf2 ratio and HIF-1α levels, without altering H2S. The late phase of cardioprotection of RIPC involves an increase in the activity of H2S biosynthetic enzymes, which increases the levels of H2S to upregulate HIF-1α and Nrf2. H2S has the potential to restore aging-induced loss of cardioprotective effects of RIPC by upregulating HIF-1α/Nrf2 signaling.

Two Compound Heterozygous Were Identified in SLC26A4 Gene in Two Chinese Families With Enlarged Vestibular Aqueduct

Yongbo Yu,Yang Yang,Jie Lu,Yaqiong Jin,Yeran Yang,Enyu Hong,Jin Shi,Feng Chen,Shujing Han,Ping Chu,Yongli Guo,Xin Ni 대한이비인후과학회 2019 Clinical and Experimental Otorhinolaryngology Vol.12 No.1

Objectives. To investigate the genetic causes of hearing loss with enlarged vestibular aqueduct (EVA) in two children from unrelated two Chinese families. Methods. Sanger sequencing of all coding exons in SLC26A4 (encoding Pendrin protein) was performed on the two patients, their sibling and parents respectively. To predict and visualize the potential functional outcome of the novel variant, model building, structure analysis, and in silico analysis were further conducted. Results. The results showed that the proband from family I harbored a compound heterozygote of SLC26A4 c.1174A>T (p.N392Y) mutation and c.1181delTCT (p.F394del) variant in exon 10, potentially altering Pendrin protein structure. In family II, the proband was identified in compound heterozygosity with a known mutation of c.919-2A>G in the splice site of intron 7 and a novel mutation of c.1023insC in exon 9, which results in a frameshift and translational termination, consequently leading to truncated Pendrin protein. Sequence homology analysis indicated that all the mutations localized at high conservation sites, which emphasized the significance of these mutations on Pendrin spatial organization and function. Conclusion. In summary, this study revealed two compound heterozygous mutations (c.1174A>T/c.1181delTCT; c.919-2A>G/c.1023insC) in Pendrin protein, which might account for the deafness of the two probands clinically diagnosed with EVA. Thus this study contributes to improve understanding of the causes of hearing loss associated with EVA and develop a more scientific screening strategy for deafness.

Kinetics and computational docking studies on the inhibition of tyrosinase induced by oxymatrine.

Liu, Xiao-Xia,Sun, Shi-Qing,Wang, Yu-Jie,Xu, Wei,Wang, Yi-Fang,Park, Daeui,Zhou, Hai-Meng,Han, Hong-Yan Humana Press 2013 Applied biochemistry and biotechnology Vol.169 No.1

<P>A combination of enzymatic inhibition kinetics and computational prediction was employed to search for an effective inhibitor of tyrosinase. We found that oxymatrine significantly inhibited tyrosinase, and that this reaction was not accompanied by detectable conformational changes. Kinetic analysis showed that oxymatrine reversibly inhibited tyrosinase in a mixed-type manner. Measurements of intrinsic and ANS-binding fluorescences showed that oxymatrine did not induce any conspicuous changes in the tertiary structure. We also conducted a docking simulation between tyrosinase and oxymatrine using two docking programs, Dock6.3 and AutoDock4.2 (binding energy was -118.81 kcal/mol for Dock6 and -8.04 kcal/mol for AutoDock4). The results also suggested that oxymatrine interacts mostly with the residues of CYS83 and HIS263 in the active site of tyrosinase. This strategy of predicting tyrosinase inhibition by simulation of docking coupling with kinetics may prove useful in screening for potential tyrosinase inhibitors. Knowledge of tyrosinase inhibition can provide medical, cosmetic, and agricultural applications. Our study suggests that oxymatrine is an important agent for various applications related to pigment formation.</P>