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RISS 인기검색어
- 검색키워드
- 저자 : Yawen Qi (검색결과 3 건)
- 무료
- 기관 내 무료
- 유료
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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.
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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.
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The effects of cigarettes and alcohol on intestinal microbiota in healthy men
Lin Renbin,Zhang Yawen,Chen Luyi,Qi Yadong,He Jiamin,Hu Mengjia,Zhang Ying,Fan Lina,Yang Tao,Wang Lan,Si Misi,Chen Shujie 한국미생물학회 2020 The journal of microbiology Vol.58 No.11
Human intestinal microbiota is affected by the exogenous microenvironment. This study aimed to determine the effects of cigarettes and alcohol on the gut microbiota of healthy men. In total, 116 healthy male subjects were enrolled and divided into four groups: non-smoking and non-drinking (Group A), smoking only (Group B), drinking only (Group C), and smoking and drinking combined (Group D). Fecal samples were collected and sequenced using 16S rRNA to analyze the microbial composition. Short-chain fatty acid (SCFAs) levels in feces were determined by gas chromatography. We found that cigarette and alcohol consumptions can alter overall composition of gut microbiota in healthy men. The relative abundances of phylum Bacteroidetes and Firmicutes and more than 40 genera were changed with cigarette and alcohol consumptions. SCFAs decreased with smoking and alcohol consumption. Multivariate analysis indicated that when compared with group A, group B/C/D had higher Bacteroides, and lower Phascolarctobacterium, Ruminococcaceae_ UCG-002, Ruminococcaceae_UCG-003, and Ruminiclostridium_ 9 regardless of BMI and age. Additionally, the abundance of Bacteroides was positively correlated with the smoking pack-year (r = 0.207, p < 0.05), the abundance of predicted pathway of bacterial toxins (r = 0.3672, p < 0.001) and the level of carcinoembryonic antigen in host (r = 0.318, p < 0.01). Group D shared similar microbial construction with group B, but exerted differences far from group C with lower abundance of Haemophilus. These results demonstrated that cigarette and alcohol consumption separately affected the intestinal microbiota and function in healthy men; furthermore, the co-occurrence of cigarette and alcohol didn’t exacerbate the dysbiosis and cigarette played the predominated role on the alteration.
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