A Virtual RLC Active Damping Method for LCL-Type Grid-Connected Inverters

Yiwen Geng,Yawen Qi,Pengfei Zheng,Fei Guo,Xiang Gao 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.5

Proportional capacitor–current–feedback active damping (AD) is a common damping method for the resonance of LCL-type grid-connected inverters. Proportional capacitor–current–feedback AD behaves as a virtual resistor in parallel with the capacitor. However, the existence of delay in the actual control system causes impedance in the virtual resistor. Impedance is manifested as negative resistance when the resonance frequency exceeds one-sixth of the sampling frequency (fs/6). As a result, the damping effect disappears. To extend the system damping region, this study proposes a virtual resistor–inductor–capacitor (RLC) AD method. The method is implemented by feeding the filter capacitor current passing through a band-pass filter, which functions as a virtual RLC in parallel with the filter capacitor to achieve positive resistance in a wide resonance frequency range. A combination of Nyquist theory and system close-loop pole-zero diagrams is used for damping parameter design to obtain optimal damping parameters. An experiment is performed with a 10 kW grid-connected inverter. The effectiveness of the proposed AD method and the system’s robustness against grid impedance variation are demonstrated.

A Virtual RLC Active Damping Method for LCL-Type Grid-Connected Inverters

Geng, Yiwen,Qi, Yawen,Zheng, Pengfei,Guo, Fei,Gao, Xiang The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.5

Proportional capacitor-current-feedback active damping (AD) is a common damping method for the resonance of LCL-type grid-connected inverters. Proportional capacitor-current-feedback AD behaves as a virtual resistor in parallel with the capacitor. However, the existence of delay in the actual control system causes impedance in the virtual resistor. Impedance is manifested as negative resistance when the resonance frequency exceeds one-sixth of the sampling frequency ($f_s/6$). As a result, the damping effect disappears. To extend the system damping region, this study proposes a virtual resistor-inductor-capacitor (RLC) AD method. The method is implemented by feeding the filter capacitor current passing through a band-pass filter, which functions as a virtual RLC in parallel with the filter capacitor to achieve positive resistance in a wide resonance frequency range. A combination of Nyquist theory and system close-loop pole-zero diagrams is used for damping parameter design to obtain optimal damping parameters. An experiment is performed with a 10 kW grid-connected inverter. The effectiveness of the proposed AD method and the system's robustness against grid impedance variation are demonstrated.

The Role of Switching Costs in O2O Platforms: Antecedents and Consequences

Minghui Kang,Yiwen Gao,Tao Wang,Meng Wang 보안공학연구지원센터 2015 International Journal of Smart Home Vol.9 No.3

Online to offline is a new business mode combining the online shopping and the front line transactions. No previous studies have simultaneously examined these variables as antecedents of e-loyalty intention or the possible relationships among them within O2O platform. Our paper has examined the effects of inertia; perceived ease of use, customization and quality of offering on the consumer’s switching costs. These findings provide a theoretical foundation for academics and also practical guidelines for service providers in dealing with the promotion of loyalty at O2O platforms.

Paridis Saponins Inhibiting Carcinoma Growth and Metastasis In Vitro and In Vivo

Shuli Man,Wenyuan Gao,Yanjun Zhang,Chaoyi Ma,Liu Yang,Yiwen Li 대한약학회 2011 Archives of Pharmacal Research Vol.34 No.1

Paris polyphylla Smith var. yunnanensis extracts, Rhizoma Paridis saponins (RPS) have been found to show strong antitumor activity. However, few studies have yet investigated pulmonary metastasis treatment with this herb. To detail the effective components in RPS and discuss the preliminary mechanism of antitumor effects in vivo and in vitro, a mixture isolated from RPS was investigated. The main constituents were identified as polyphyllin D, formosanin C, dioscin, Paris H, Paris VII and pennogennin 3-O-α-L-rhamnopyranosyl (1→4)-[β-L-rhamnopyranosyl (1→2)]-β-D-glucopyranoside. In our experiments, LA795 cells were exposed to the mixed compounds. Migration inhibition was evaluated by wound healing assay and migration assay in non-cytotoxic dose which was determined by MTT assay. The results demonstrated that the constituent in varying degrees inhibited the migration of the tumor cells in vitro. The mixture also showed antitumor effects on carcinoma in vivo. In conclusion, the mixture is a potent anticancer agent that elicits programmed cell death and inhibits the migration in murine lung adenocarcinoma, both in vitro and in vivo.

Ginsenosides Rg1 regulate lipid metabolism and temperature adaptation in Caenorhabditis elegans

Hao Shi,Jiamin Zhao,Yiwen Li,Junjie Li,Yunjia Li,Jia Zhang,Zhantu Qiu,Chaofeng Wu,Mengchen Qin,Chang Liu,Zhiyun Zeng,Chao Zhang,Lei Gao 고려인삼학회 2023 Journal of Ginseng Research Vol.47 No.4

Graded-Three-Dimensional Cell-Encapsulating Hydrogel as a Potential Biologic Scaffold for Disc Tissue Engineering

Li Zhixiang,Zhang Yiwen,Zhao Yupeng,Gao Xubin,Zhu Zhonglian,Mao Yingji,Qian Taibao 한국조직공학과 재생의학회 2022 조직공학과 재생의학 Vol.19 No.5

BACKGROUND: Intervertebral disk (IVD) degeneration, which can cause lower back pain, is a major predisposing factor for disability and can be managed through multiple approaches. However, there is no satisfactory strategy currently available to reconstruct and recover the natural properties of IVDs after degeneration. As tissue engineering develops, scaffolds with embedded cell cultures have proved critical for the successful regeneration of IVDs. METHODS: In this study, an integrated scaffold for IVD replacement was developed. Through scanning electron microscopy and other mechanical measurements, we characterized the physical properties of different hydrogels. In addition, we simulated the physiological structure of natural IVDs. Nucleus pulposus (NP) cells and annulus fibrosusderived stem cells (AFSCs) were seeded in gelatin methacrylate (GelMA) hydrogel at different concentrations to evaluate cell viability and matrix expression. RESULTS: It was found that different concentrations of GelMA hydrogel can provide a suitable environment for cell survival. However, hydrogels with different mechanical properties influence cell adhesion and extracellular matrix component type I collagen, type II collagen, and aggrecan expression. CONCLUSION: This tissue-engineered IVD implant had a similar structure and function as the native IVD, with the inner area mimicking the NP tissue and the outer area mimicking the stratified annulus fibrosus tissue. The new integrated scaffold demonstrated a good simulation of disc structure. The preparation of efficient and regeneration-promoting tissueengineered scaffolds is an important issue that needs to be explored in the future. It is hoped that this work will provide new ideas and methods for the further construction of functional tissue replacement discs.

Trimethyl-Ammonium Alkaline Anion Exchange Membranes with the Vinylbenzyl Chloride/Acrylonitrile Main Chain

Zhenghan Li,Junjie Chen,JinYue Zhou,YiWen Nie,Chunhui Shen,Shanjun Gao 한국고분자학회 2021 Macromolecular Research Vol.29 No.7

The main chain of polyolefin was synthesized by copolymerization of 4 - vinylbenzyl chloride (VBC) and acrylonitrile (AN), and trimethylamine is used for quaternization to prepare heterogeneous benzyl trimethyl-ammonium anion exchange membranes (Heter-X) and homogeneous benzyl trimethyl-ammonium anion exchange membrane (Homo-X). The results of Fourier-transform infrared (FT-IR), gel permeation chromatography (GPC), and 1H nuclear magnetic resonance (NMR) showed that VBC and AN were successfully copolymerized to form a polymer with a certain molecular weight, and trimethylamine was successfully quaternized. The prepared membranes exhibited good thermal stability and mechanical properties. The theoretical ion exchange capacity (IEC) values of Homo-3 and Heter-3 are the same, but the conductivity at 80 °C were 0.0572 S cm-1 and 0.0505 S cm-1. The results showed that the homogeneous method has a higher degree of quaternization and a more uniform distribution of quaternary ammonium groups, forming a more obvious microphase separation structure, which can also be seen in the atomic force microscopy (AFM) diagram. After being soaked in 1M KOH solution for 480 h, the ionic conductivity of Homo-6 and Heter-6 can still remain 91.4% and 85.5%, and the IEC loss rates were 17.21% and 24.34%. These results indicate that the prepared membranes are promising materials for application in fuel cells.

ZntR positively regulates T6SS4 expression in Yersinia pseudotuberculosis

Tietao Wang,Keqi Chen,Fen Gao,Yiwen Kang,Muhammad Tausif Chaudhry,Zhuo Wang,Yao Wang,Xihui Shen 한국미생물학회 2017 The journal of microbiology Vol.55 No.6

The type VI secretion system (T6SS) is a widespread and versatile protein secretion system found in most Gram- negative bacteria. Studies of T6SS have mainly focused on its role in virulence toward host cells and inter-bacterial inter-actions, but studies have also shown that T6SS4 in Yersinia pseudotuberculosis participates in the acquisition of zinc ions to alleviate the accumulation of hydroxyl radicals induced by multiple stressors. Here, by comparing the gene expression patterns of wild-type and zntR mutant Y. pseudotubercu-losis cells using RNA-seq analysis, T6SS4 and 17 other bio-logical processes were found to be regulated by ZntR. T6SS4 was positively regulated by ZntR in Y. pseudotuberculosis, and further investigation demonstrated that ZntR regulates T6SS4 by directly binding to its promoter region. T6SS4 ex-pression is regulated by zinc via ZntR, which maintains in-tracellular zinc homeostasis and controls the concentration of reactive oxygen species to prevent bacterial death under oxidative stress. This study provides new insights into the regulation of T6SS4 by a zinc-dependent transcriptional regu-lator, and it provides a foundation for further investigation of the mechanism of zinc transport by T6SS.