Soft-Switching T-Type Multilevel Inverter

Tianyu Chen,Mehdi Narimani 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.5

In order to improve the conversion efficiency and mitigate the EMI problem of conventional hard-switching inverters, a new soft-switching DC-AC inverter with a compact structure and a low modulation complexity is proposed in this paper. In the proposed structure, resonant inductors are connected in series for the arm branches, and resonant capacitors are connected in parallel for the neutral point branches. With the help of resonant components, the proposed structure achieves zero-current switching on the arm branches and zero-voltage switching on the neutral point branches. When compared with state-of-art soft-switching topologies, the proposed topology does not need auxiliary switches. Moreover, the commutation algorithm to realize soft-switching can be easily implemented. In this paper, the principle of the resonant operation of the proposed soft-switching converter is presented and its performance is verified through simulation studies. The feasibility of the proposed inverter is evaluated experimentally with a 2.4-kW prototype.

Soft-Switching T-Type Multilevel Inverter

Chen, Tianyu,Narimani, Mehdi The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.5

In order to improve the conversion efficiency and mitigate the EMI problem of conventional hard-switching inverters, a new soft-switching DC-AC inverter with a compact structure and a low modulation complexity is proposed in this paper. In the proposed structure, resonant inductors are connected in series for the arm branches, and resonant capacitors are connected in parallel for the neutral point branches. With the help of resonant components, the proposed structure achieves zero-current switching on the arm branches and zero-voltage switching on the neutral point branches. When compared with state-of-art soft-switching topologies, the proposed topology does not need auxiliary switches. Moreover, the commutation algorithm to realize soft-switching can be easily implemented. In this paper, the principle of the resonant operation of the proposed soft-switching converter is presented and its performance is verified through simulation studies. The feasibility of the proposed inverter is evaluated experimentally with a 2.4-kW prototype.

Ultrafast Channel II process induced by a 3-D texture with enhanced acceptor order ranges for high-performance non-fullerene polymer solar cells

Chen, Shanshan,Lee, Sang Myeon,Xu, Jianqiu,Lee, Jungho,Lee, Kyu Cheol,Hou, Tianyu,Yang, Yankang,Jeong, Mingyu,Lee, Byongkyu,Cho, Yongjoon,Jung, Sungwoo,Oh, Jiyeon,Zhang, Zhi-Guo,Zhang, Chunfeng,Xiao, The Royal Society of Chemistry 2018 ENERGY AND ENVIRONMENTAL SCIENCE Vol.11 No.9

<P>To achieve efficient non-fullerene polymer solar cells (NF-PSCs), an in-depth understanding of the key properties that govern the power output is necessary. Herein, three trialkylsilyl substituted benzodithiophene-based polymer donors (PJ1, PJ2, and PJ3) were synthesized with fine-tuning of the highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) and optical absorption. Using the polymer series paired with absorption-complementary small molecular acceptors (SMAs), namely, <I>m</I>-ITIC, IDIC, and AIDIC, we systematically studied the performance of a 3 × 3 matrix of NF-PSCs. An increasing open-circuit voltage with deepening HOMOs of the polymer donors, and the enhanced short-circuit current (<I>J</I>SC) and fill factor (FF) were ascribed to the well-intermixed blend morphology containing enhanced SMA order ranges with mixed face-on and edge-on orientations, the so-called 3-D texture. Such an optimal microstructure is best exemplified in the PJ2:IDIC combination, affording a highest efficiency of 12.01% with a simultaneously high <I>J</I>SC of 17.0 mA cm<SUP>−2</SUP> and FF of 75.3%. The devices with an active layer thickness of 300 nm still maintain an impressive efficiency approaching 10% with a decent FF of 60.0%. Moreover, the Channel II process, <I>i.e.</I>, photoinduced hole transfer through acceptor excitation, was demonstrated to be crucially important for photocurrent generation. This study highlights the importance of optimizing the trade-off between charge separation/transport and domain size to achieve high-performance NF-PSCs.</P>

Damping for Wind Turbine Electrically Excited Synchronous Generators

Tianyu, Wang,Guojie, Li,Yu, Zhang,Chen, Fang The Korean Institute of Electrical Engineers 2016 Journal of Electrical Engineering & Technology Vol.11 No.4

The electrically excited synchronous generator (EESG) is applied in wind turbine systems recently. In an EESG control system, electrical torque is affected by stator flux and rotor current. So the control system is more complicated than that of the permanent-magnet synchronous generator (PMSG). Thus, the higher demanding of the control system is required especially in case of wind turbine mechanical resonance. In this paper, the mechanism of rotor speed resonant phenomenon is introduced from the viewpoint of mechanics firstly, and the characteristics of an effective damping torque are illustrated through system eigenvalues analysis. Considering the variables are tightly coupled, the four-order small signal equation for torque is derived considering stator and rotor control systems with regulators, and the bode plot of the closed loop transfer function is analyzed. According to the four-order mathematical equation, the stator flux, stator current, and electrical torque responses are derived by torque reference step and ramp in MATLAB from a pure mathematical deduction, which is identical with the responses in PSCAD/EMTDC simulation results. At last, the simulation studies are carried out in PSCAD software package to verify the resonant damping control strategy used in the EESG wind turbine system.

Field investigation of the reinforcement and support mechanism for a tunnel in layered soft rock mass

Yulong Chen,Zhe Li,Tianyu Cui 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.10

A crucial deformation phenomenon is observed in shale and silty clay sections in a tunnel. To analyse the reinforcement and support mechanism and behaviour of the tunnel support structure in layered soft rocks, field tests for the axial force of the cartridge rock bolt, surrounding rock pressure, stress of a steel I-beam and lattice girder were performed. Based on the field deformation analysis data, the reinforcement behaviours of the cartridge rock bolt and steel floral pipe, and support behaviours of lattice girder and steel I-beam in the layered rock mass and silty clay were analysed.

Profiling Total Viable Bacteria in a Hemodialysis Water Treatment System

( Lihua Chen ),( Xuan Zhu ),( Menglu Zhang ),( Yuxin Wang ),( Tianyu Lv ),( Shenghua Zhang ),( Xin Yu ) 한국미생물 · 생명공학회 2017 Journal of microbiology and biotechnology Vol.27 No.5

Culture-dependent methods, such as heterotrophic plate counting (HPC), are usually applied to evaluate the bacteriological quality of hemodialysis water. However, these methods cannot detect the uncultured or viable but non-culturable (VBNC) bacteria, both of which may be quantitatively predominant throughout the hemodialysis water treatment system. Therefore, propidium monoazide (PMA)-qPCR associated with HPC was used together to profile the distribution of the total viable bacteria in such a system. Moreover, high-throughput sequencing of 16S rRNA gene amplicons was utilized to analyze the microbial community structure and diversity. The HPC results indicated that the total bacterial counts conformed to the standards, yet the bacteria amounts were abruptly enhanced after carbon filter treatment. Nevertheless, the bacterial counts detected by PMA-qPCR, with the highest levels of 2.14 × 107 copies/100 ml in softener water, were much higher than the corresponding HPC results, which demonstrated the occurrence of numerous uncultured or VBNC bacteria among the entire system before reverse osmosis (RO). In addition, the microbial community structure was very different and the diversity was enhanced after the carbon filter. Although the diversity was minimized after RO treatment, pathogens such as Escherichia could still be detected in the RO effluent. In general, both the amounts of bacteria and the complexity of microbial community in the hemodialysis water treatment system revealed by molecular approaches were much higher than by traditional method. These results suggested the higher health risk potential for hemodialysis patients from the up-to-standard water. The treatment process could also be optimized, based on the results of this study.

Effect of curing cycles using wet prepreg processing on mechanical properties

Zixuan, Chen,Tianyu, Yu,Jung, Kyung-Seok,Park, Chang-Wook,Park, Soo-Jeong,Koinkar, Pankaj,Kim, Yun-Hae World Scientific Publishing Company 2018 International Journal of Modern Physics B Vol.32 No.19

<P>For the fabrication of polymer-based composite materials, the interpretation of an appropriate fabrication process is essential to improve the productivity and manufacturing process. In this study, the wet prepreg forming process was used to fabricate carbon fiber reinforced plastic (CFRP) and different curing cycles were demonstrated for an optimal process. To determine the range of curing temperature, a pretreatment on differential scanning calorimetry (DSC) analysis was performed. After that, tensile and ILSS tests were adopted to investigate the mechanical properties and thermal analysis on a matrix carried out by the DSC equipment. Different volumes of the matrix residue on fractured fiber, which represent the matrix-reinforcement adhesion strength, were observed by a scanning electron microscope (SEM). Also, a void aggregation was found in high curing temperature situation due to excessive exotherm. Both the tensile strength and ILSS held a certain trend with the changing curing cycles. The highest tensile strength (469 MPa) and glass transition temperature (Tg) at 91.58<TEX>$ ^{\circ }$</TEX>C occurred at 80<TEX>$ ^{\circ }$</TEX>C and 12 h curing temperature and time, respectively. The result of ILSS had an almost opposite tendency of the tensile strength. A correlation between Tg and mechanical properties was observed and it can be extensively applied to optimize the manufacturing process.</P>

Damping for Wind Turbine Electrically Excited Synchronous Generators

Wang Tianyu,Li Guojie,Zhang Yu,Fang Chen 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.4

The electrically excited synchronous generator (EESG) is applied in wind turbine systems recently. In an EESG control system, electrical torque is affected by stator flux and rotor current. So the control system is more complicated than that of the permanent-magnet synchronous generator (PMSG). Thus, the higher demanding of the control system is required especially in case of wind turbine mechanical resonance. In this paper, the mechanism of rotor speed resonant phenomenon is introduced from the viewpoint of mechanics firstly, and the characteristics of an effective damping torque are illustrated through system eigenvalues analysis. Considering the variables are tightly coupled, the four-order small signal equation for torque is derived considering stator and rotor control systems with regulators, and the bode plot of the closed loop transfer function is analyzed. According to the four-order mathematical equation, the stator flux, stator current, and electrical torque responses are derived by torque reference step and ramp in MATLAB from a pure mathematical deduction, which is identical with the responses in PSCAD/EMTDC simulation results. At last, the simulation studies are carried out in PSCAD software package to verify the resonant damping control strategy used in the EESG wind turbine system.

Seismic Performance of a Subway Station-Tunnel Junction Structure: A Shaking Table Investigation and Numerical Analysis

Qingjun Chen,Tianyu Zhang,Na Hong,Bin Huang 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.5

Damage cases show that during earthquakes, the sharp stiffness mutation of subway station-tunnel junction structures can lead to dislocations at the connections. To address this, shaking table tests were conducted followed by numerical simulations of a typical junction structure with rigid connections. The modeling method was verified based on the test results. Furthermore, numerical models of junction structures with rigid and flexible connections, single stations, and single tunnels were built, and deformation modes and stress distributions were comparatively analyzed. Combining the experimental and numerical results, it is found that there exists an intensive deformation inconsistency between the stations and the tunnels responsible for the junction structures’ dislocation failures. The station operates in both racking and distortion deformation modes when the tunnel undergoes ovaling deformation. The tunnel bends relative to the end wall at the connection. The junction structure with rigid connections is most at risk at the point located at the tunnel section connected to the end wall and near the bottom plate-sidewall joint. With flexible connections, the tunnels integrally translate relative to the end wall, and the stress response of the end wall openings can be larger than those with rigid connections.

Simultaneous Impact of Multiple Droplets on Liquid Film

Gangtao Liang,Tianyu Zhang,Haibing Yu,Hongliang Chen,Shengqiang Shen 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.65 No.-

Multiple droplets impinging on a thin liquid film simultaneously is numerically studied using a three-dimensional model with an implement of a random disturbance subjected to Gaussian distribution. This model is very effective to predict droplet splashing under relatively high impingement momentum. Interface evolutions and field distributions are addressed after droplets impact. Besides, a geometric model is built up to demarcate the impact region into two semicircular regions and a series of rectangular regions during simultaneous impact, further to discuss the variations of area and residual film thickness in each region as well as the total area and average film thickness.