Novel Buck Mode Three-Level Direct AC Converter with a High Frequency Link

Li, Lei,Guan, Yue,Gong, Kunshan,Li, Guangqiang,Guo, Jian The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.2

A novel family of Buck mode three-level direct ac converters with a high frequency link is proposed. These converters can transfer an unsteady high ac voltage with distortion into a regulated sinusoidal voltage with a low THD at the same frequency. The circuit configuration is constituted of a three-level converter, high frequency transformer, cycloconverter, as well as input and output filters. The topological family includes forward, push-pull, half-bridge, and full-bridge modes. In order to achieve a reliable three-level ac-ac conversion, and to overcome the surge voltage and surge current of the cycloconverter, a phase-shifted control strategy is introduced in this paper. A prototype is presented with experimental results to demonstrate that the proposed converters have five advantages including high frequency electrical isolation, lower voltage stress of the power switches, bi-directional power flow, low THD of the output voltage, and a higher input power factor.

Novel Buck Mode Three-Level Direct AC Converter with a High Frequency Link

Lei Li,Yue Guan,Kunshan Gong,Guangqiang Li,Jian Guo 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.2

A novel family of Buck mode three-level direct ac converters with a high frequency link is proposed. These converters can transfer an unsteady high ac voltage with distortion into a regulated sinusoidal voltage with a low THD at the same frequency. The circuit configuration is constituted of a three-level converter, high frequency transformer, cycloconverter, as well as input and output filters. The topological family includes forward, push-pull, half-bridge, and full-bridge modes. In order to achieve a reliable three-level ac-ac conversion, and to overcome the surge voltage and surge current of the cycloconverter, a phase-shifted control strategy is introduced in this paper. A prototype is presented with experimental results to demonstrate that the proposed converters have five advantages including high frequency electrical isolation, lower voltage stress of the power switches, bi-directional power flow, low THD of the output voltage, and a higher input power factor.

Microstructural Refinement and Performance Improvement of Cast n-Type Bi2Te2.79Se0.21 Ingot by Equal Channel Angular Extrusion

Xiaoming Hu,Xi’an Fan,Bo Feng,Dong Kong,Peihai Liu,Rusong Li,Yanglin Zhang,Guangqiang Li,Yawei Li 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.8

How to form a uniform fine-grained structure in n-type polycrystalline Bi2Te3based alloys to stabilize and improve thethermoelectric properties is the burning issue to be solved. In the present work, equal channel angular extrusion (ECAE)method was used to extrude the cast ingot directly at various temperatures to obtain the BiTeSe polycrystalline bulk alloyswith uniform microstructure. The initial lamellae coarse grains (hundreds microns to several millimeters) were efficiently anduniformly refined to a minimum of 4.07 μm at 703 K, which fully demonstrates the feasibility of grain refinement by ECAEfor cast n-type BiTeSe ingot. The average grain size of the extruded billets rapidly increased from 5.35 to 29.55 μm withthe increase of extrusion temperature from 703 to 823 K. Meanwhile, the behavior of abnormal grain growth became moreevident as the extrusion temperature increased because the growth rate increased more rapidly than the rate of nucleation. As the extrusion temperature increased, the Vickers hardness decreased gradually due to grain coarsening. BiTeSe alloysextruded at 703 K achieved the maximum Vickers hardness of 59.8 HV0.05,which was nearly three times higher than that ofthe initial cast ingot. All extruded BiTeSe billets possessed the much higher dimensionless figure of merit (ZT), comparedwith the initial cast ingot due to the simultaneously optimization of electrical and thermal transport performances caused byECAE process. Finally, the specimen extruded at 823 K achieved the maximum ZT of 0.685 at 383 K.

Effect of Thread Count on the Shear Mechanical Properties and Dynamic Mechanical Properties of Shape Memory Polymer Reinforced by Single-Ply Weave Fabric

Peng Qu,Guangqiang Fang,He Kong,Zhengli Cao,Jia Ma,Zhiyi Wang,An-Fu Guo,Shaoqing Wang,Xunjin Li,Xinran Shan 한국섬유공학회 2023 Fibers and polymers Vol.24 No.9

Shape memory epoxy polymer reinforced by single-ply weave fabric (SMEP-W) possesses high specific stiffness, good foldability, and satisfactory shape memory capability. These advantages make them promising materials for deployable space structures and increasingly attract research interests. Understanding the influence of weave structures on static and dynamic mechanical properties is crucial to structural design and mechanical response prediction. In this paper, a recently developed SMEP-W was prepared. The static shear experiments were conducted through modified shear test fixtures, and the stress field under static shear load was simulated through a multi-scale numerical modelling method. The dynamic mechanical analysis was carried out to evaluate the shape memory capability. SMEP-W shows nonlinear mechanical behavior under in-plane shear load, especially for the one with less thread count. The increase in the number of threads enhances the constraints between warp yarns and weft yarns, leading to an increase in shear modulus and reducing the scattering of static mechanical properties. The stress distribution on the yarns has the characteristic of center symmetry. High-stress regions appear on the overlapping surface of the crossover regions. Compared with shape memory epoxy polymer (SMEP), the glass transition temperature and damping coefficient of SMEP-W are significantly reduced, and the stiffness is remarkably enhanced. The difference in thread count between warp direction and weft direction does not notably affect the glass transition temperature and tan δ, but has a remarkable influence on the storage modulus. The present work could provide basic observation for understanding the influence of thread count on the shear mechanical properties and dynamic mechanical properties of SMEP-W.

In-Situ Observation of Grain Refinement in the Simulated Heat-Affected Zone of High-Strength Low-Alloy Steel by Zr-Ti Combined Deoxidation

Bowen Zhou,Guangqiang Li,Xiangliang Wan,Yu Li,Kaiming Wu 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.2

The effect of Zr-Ti combined deoxidation on the grain refinement in the simulated coarse-grained heat-affected zone of a high-strength low-alloy steel was investigated by means of analytical characterization techniques such as in-situ microscopy, transmission electron microscopy, and electron backscattered diffraction analysis. Owing to the Zr-Ti combined deoxidation, a large amount of fine Zr-Ti oxide particles were formed in the steel and retarded the austenite grain growth during simulated welding thermal cycle. The austenite grains were small and uniform. The Mn can diffuse spontaneously from austenite to Zr-Ti oxide inclusion and MnS precipitated on ZrO2, which can form Mn depleted zone in the vicinity of inclusion. The acicular ferrite grains nucleated on intragranular Zr-Ti oxide inclusions in austenite grains grew in different directions and effectively divided the austenite grain into several finer and separate regions at intermediate temperature. The crystallographic grain size became small in the simulated coarse-grained heat-affected zone of Zr-Ti-killed steel due to the effective pinning effect by Zr-Ti oxide particles and acicular ferrite formation.

Research Progress of Hydrostatic Bearing and Hydrostatic-Hydrodynamic Hybrid Bearing in High-End Computer Numerical Control Machine Equipment

Xiaodong Yu,Weicheng Gao,Yanan Feng,Guangqiang Shi,Shihao Li,Minmin Chen,Ruiming Zhang,Junfeng Wang,Wentao Jia,Jianhua Jiao,Ruichun Dai 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.6

Hydrostatic bearing has the advantages of wide speed range, large bearing capacity, high precision and stability. Hydrostatic-hydrodynamic hybrid bearing can make up for the lack of stiffness of hydrostatic bearing and prevent tribological failure under the condition of high speed and heavy load. Therefore, hydrostatic bearing and hydrostatic-hydrodynamic hybrid bearing have become important bearing parts of high-end computer numerical control (CNC) machine equipment. The research on hydrostatic and hydrostatic-hydrodynamic open a new way for precision improvement of high-end CNC machine equipment. This paper reviews research progress of hydrostatic linear guideway, hydrostatic rest and ram, hydrostatic thrust bearing, hydrostatic-hydrodynamic thrust bearing and hydrostatic-hydrodynamic spindle of high-end CNC machine equipment, and discusses the influence of structure and working parameters on lubrication performance, accuracy and stability of bearing parts. Finally, the future research direction in hydrostatic bearing and hydrostatic-hydrodynamic hybrid bearing are suggested. This review provides a theoretical basis for design and development of high-end CNC machine equipment in the future.

Piperonyl butoxide synergizes the larvicidal activity of Origanum vulgare essential oil and its major constituents against the larvae of Aedes albopictus and Culex pipiens quinquefasciatus

Chen Junhui,Liu Yangqing,Ma Guangqiang,Yang Feiying,Zhan Zhigao,Guan Limei,Kuang Wendong,Wang Jinchang,Li Jianghuai,Han Fei,Jin Liang 한국응용곤충학회 2023 Journal of Asia-Pacific Entomology Vol.26 No.1

Mosquitoes bite human beings and transmit many diseases, such as malaria, dengue fever, and Zika virus. Vector control of mosquitoes is an effective strategy for reducing the spread of disease. However, extensive use of in secticides (e.g. pyrethroids and organophosphorus) has caused resistance in mosquitoes, which weakens the effectiveness of mosquito control. Phytochemicals have been considered an alternative approach to mosquito control. Essential oil (EO) was obtained from the leaves and flowers of Origanum vulgare, and its synergistic activity with piperonyl butoxide (PBO) was tested against Aedes albopictus and Culex pipiens quinquefasciatus larvae. Thirty-seven compounds were identified, among which carvacrol and thymol were two major constitu ents (30.73 % and 18.81 %, respectively). O. vulgare EO had a significant toxic effect against fourth-stage larvae of Cx. p. quinquefasciatus and Ae. albopictus, with LC 50 values of 17.51 and 75.90 mg/L. Carvacrol and thymol also each appeared to be more effective against Cx. p. quinquefasciatus (LC 50 = 19.30 and 11.56 mg/L, respectively) than Ae. albopictus (LC 50 = 26.62 and 26.66 mg/L, respectively). PBO interacted synergistically with O. vulgare EO, carvacrol and thymol with 2.60–6.26 times as much of the active compound needed without PBO as against Cx. p. quinquefasciatus and Ae. albopictus larvae. Overall, our results contribute to the development of new natural mosquito insecticides.

Magnetic alignment of MnBi crystals and magnetic properties of MnBi-Bi composites

Yongsheng Liu,Jincang Zhang,Zhongming Ren,Shixun Cao,Xiaoyong Zhang,Guangqiang Jia,Kang Deng,Xi Li,Junxi Zhang 한국물리학회 2007 Current Applied Physics Vol.7 No.5

Below Curie temperatureTC, MnBi crystals are aligned alongc-axis in a Bi matrix under a fabrication eldHfof 0.5 T. AboveTC,this alignment is also accomplished by quenching under a highHfof 10 T. Such a method has a prominent feature that MnBi crystalsgrow preferentially and congregate along theHfdirection. Magnetic testing shows a pronounced anisotropy in magnetization in direc-tions normal and parallel toHf, resulting from the alignment. In the case of the alignment belowTC,Hfincreases the transition temper-ature of spin-reorientation and the change in magnetization.