Quasi-Fixed-Frequency Hysteresis Current Tracking Control Strategy for Modular Multilevel Converters

Mei, Jun,Ji, Yu,Du, Xiaozhou,Ma, Tian,Huang, Can,Hu, Qinran The Korean Institute of Power Electronics 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.6

This study proposes a quasi-fixed-frequency hysteresis current tracking control strategy for modular multilevel converters (MMCs) on the basis of voltage partition principle. First, by monitoring the grid voltage and the deviation between the output and reference currents, the output voltage is determined, thus prompting the output current to quickly and efficiently track the given current. Second, the voltages of the upper/lower capacitor of the arm and the voltages between the upper and lower arms are balanced by combining these arms with virtual loop mapping and arm voltage balance control, respectively. In particular, the proposed method is designed for any level and number of sub-modules. The validity of the proposed method is verified by simulations and experimental results of a five-level MMC prototype.

Association Between Psychosocial Disorders and Gastroesophageal Reflux Disease: A Systematic Review and Meta-analysis

Meijun He,Qun Wang,Da Yao,Jing Li,Guang Bai 대한소화기 기능성질환∙운동학회 2022 Journal of Neurogastroenterology and Motility (JNM Vol.28 No.2

Background/AimsThe incidence of gastroesophageal reflux disease (GERD) is increasing annually. Studies have suggested that psychosocial disorders may be linked to the development of GERD. However, studies evaluating the association between psychosocial disorders and GERD have been inconsistent. Thus, we conducted a systematic review and meta-analysis of observational studies that evaluated the association between psychosocial disorders and GERD. MethodsWe systematically searched the PubMed, Embase, Cochrane, and Web of Science databases until October 17, 2020. Pooled OR with 95% CI and subgroup analyses were calculated using a random-effects model. Subgroup analyses were performed to identify the sources of heterogeneity. Sensitivity analysis by one-study removal was used to test the robustness of our results. ResultsThis meta-analysis included 1 485 268 participants from 9 studies. Studies using psychosocial disorders as the outcome showed that patients with GERD had a higher incidence of psychosocial disorders compared to that in patients without GERD (OR, 2.57; 95% CI, 1.87-3.54; I2 = 93.8%; P < 0.001). Studies using GERD as an outcome showed an association between psychosocial disorders and an increased risk of GERD (OR, 2.23; 95% CI, 1.42-3.51; I2 = 97.1%; P < 0.001). The results of the subgroup analysis showed that the non-erosive reflux disease group had a higher increased risk of anxiety than erosive reflux disease group (OR, 9.45; 95% CI, 5.54- 16.13; I2 = 12.6%; P = 0.285). ConclusionResults of our meta-analysis showed that psychosocial disorders are associated with GERD; there is an interaction between the two.

Research on Dynamic Intelligent Information Processing Method for Distributed Generation Systems Based on Multi-Agent Techniques

Tieyan Zhang,Silin Wang,Meijun Li 보안공학연구지원센터 2016 International Journal of u- and e- Service, Scienc Vol.9 No.8

Distributed renewable energy generation is lack of intelligent information processing and decision-making section. The above problems can be solved effectively by the means of intelligent information processing technology based on the dynamic structure of multi-agent for distributed renewable energy. In order to solve the problems of less data and poor information, this paper puts forward fuzzy hyperbolic model and attempts to use dynamic intelligent information processing technology based on multi-agent to change the unreliable, inaccurate information into be full, reliable and accurate. And then the information we have obtained could be intelligent fitted, filtered and decided. The self-organizing self-learning and reasoning ability of multi-agent are considered when the information processing. The intelligent information processing section is comprised of three layers and two kinds of agents. The two kinds of agents are Bus Agents and Coordination Agents, and the three structural layers are the data layer, the filter layer and the policy making layer. Moreover the information have been processed could be utilized.

Magnetic Field Model of Macro-motion of Coaxial Integrated Macro-micro Composite Actuator

Caofeng Yu,Zhuo Chen,Meijun Xiong,Yu Wang, Rui Shi,Xiaoxiang Sun 한국자기학회 2021 Journal of Magnetics Vol.26 No.1

Transcriptome analysis of metabolisms related to fruit cracking during ripening of a cracking‑susceptible grape berry cv. Xiangfei (Vitis vinifera L.)

Mingtao Zhu,Jun Yu,Min Zhao,Meijun Wang,Guoshun Yang 한국유전학회 2020 Genes & Genomics Vol.42 No.6

Background Grape is an economically valuable fruit around the world. However, some cultivars are prone to fruit cracking during ripening, leading to severe losses. Objective We aimed to find important metabolisms related to fruit cracking during ripening process. Methods RNA-Sequence and analysis was applied to the pericarp of cracking-susceptible ‘Xiang Fei’ at 1 (W1), 2 (W2) and 3 weeks (W3) after veraison on Illumina HiSeq xten; Results Compared with W1, the berry cracking rate increased significantly in W2 and W3. Through transcriptomic analysis, a total of 22,609 genes were expressed in the grape pericarp, among which 805 and 2758 genes were significantly differentially regulated in W1-vs.-W2 and W1-vs.-W3 comparison, respectively. Besides, 304 and 354 genes were up- and down-regulated in both comparisons. The significantly enriched GO terms of both W1–W2 and W1–W3 are related to cell wall and wax biosynthesis. And lipid metabolism, which are involved in the top 20 enriched KEGG pathways of both comparisons, was related to wax biosynthesis. Further, GO enrichment analysis of differentially expressed genes (DEGs) with same regulatory changes also indicated that the continuously up-regulated DEGs are significantly enriched in cell wall component biosynthesis and hydrolase. Conclusion These findings suggested that genes related to cell wall metabolism and cuticle biosynthesis may play important roles in regulating grape berry cracking. Our results provide a reference for further studies on the molecular mechanism underlying fruit cracking.

Partial Shade Optimizes Photosynthesis and Growth in Bayberry (Myrica rubra) Trees

Guanghui Zeng,Yanping Guo,Jianxu Xu,Meijun Hu,Jie Zheng,Zhenwang Wu 한국원예학회 2017 Horticulture, Environment, and Biotechnology Vol.58 No.3

This study investigates the effects of radiation heat-load reduction under different shading conditions on thegrowth of three-year-old bayberry (Myrica rubra) trees from 1 July through 31 October 2007 in the Zhejiang Province,a warm subtropical region of China. The trees were grown under direct sunlight (control) and under 25%, 50%, and75% shading conditions using black plastic nets. Stomatal conductance and photosynthesis were greatest under 50%shading, as were plant height and leaf and root dry weights. Twenty-five percent shading did not significantly influenceplant height or root and leaf dry weights, whereas 75% shading resulted in a decrease in root and leaf dry weightswhen compared with the controls. The photochemical efficiency and electron transport of PSII increased under shadedconditions due to an increase in D1 protein. The concentrations of chlorophyll a and b and the total chlorophyllcontent in leaves were increased in plants grown under 25% and 50% shading, but reduced in those grown under75% shading. Under 50% shading, growth and biomass increased due to increased photosynthesis, which resulted fromdecreased photodamage and increased chlorophyll concentration. These data show that 50% shading promotes optimalgrowth in bayberry plants.

Rainwater Harvesting with Treatment and Utilization in an Interchange Ramp Area of Highway

Youyuan Chen,Yaping Li,Bo Hong,Meijun Feng,Bin Dong 한국도시환경학회 2010 한국도시환경학회지 Vol.10 No.2

Design of Large-Stroke and High-Resolution Drive System Based on Giant Magnetostrictive Material

Tian Xie,Chuanli Wang,Caofeng Yu,Meijun Xiong 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.5

A novel macro–micro linear actuator based on the giant magnetostrictive material has been proposed to achieve high precision and large-stroke. This structure uses a permanent magnet drive coil structure, and a new cylindrical structure permanent magnet linear actuator is made according to the principle of Lorentz force. The permanent magnet and the shell form stator part, and the giant magnetostrictive actuator (GMA) structure is embedded in the interior as a mover structure to achieve macro-motion displacement; the micro-motion can be realized by controlling the GMA. The micro-motion component and the macro-motion component can always remain coaxial in structure and integrated on a motor structure. The actuator’s output displacement can be adjusted by controlling the macro/micro coil current. Experimental results indicate that the macro-displacement can be up to 30 mm, and the response time is below 0.2 s. The micro-motion positioning accuracy can reach nanometer level, which has the advantages of simple structure and easy installation with coaxial, and has a broad application prospect in the field of precision manufacturing.

Cooling System Design Optimization of a High Power Density PM Traction Motor for Electric Vehicle Applications

Zhu Gaojia,Jia Nan,Li Longnv,Liu Tao,Xue Ming,Li Meijun 대한전기학회 2021 Journal of Electrical Engineering & Technology Vol.16 No.6

Due to the high power density characteristics of permanent magnet (PM) traction motors and the strict loading conditions of electric vehicle (EV) engine compartments, the excessive losses inside the motors can elevate rapidly the temperature rises, deteriorate the magnetic property of PMs, limit the output torques, and even cause the overheating damages of the machines. In order to guarantee the operational reliability, it’s of vital importance to research and develop the eff ective, reliable and economical cooling systems for improving the working performances of the PM traction motors. In this paper, the three-dimensional (3D) fl uidic-thermal coupled model of a high power density interior PM traction motor is established based on the basic theory of computational fl uid dynamics (CFD) and numerical heat transfer. The fl uid fl ow and thermal distributions are analyzed based on fi nite volume method (FVM), and verifi ed by experimental results. According to the heating characteristics of the motor, the external water frame structure of the motor shell is modifi ed to improve the cooling effi ciency. Taguchi method is used to optimize the cooling structural parameters, so as to reduce the steady-state temperature rise of the motor. The research work in this paper has certain reference signifi cance for the design and development of high power density PM traction motors used in EV applications.