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Voltage equalization control of three‑phase cascaded H‑bridge multilevel rectifiers
Liqiao Wang,Xuchen Chen,Zukun Zhang,Xuemeng Guo 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.2
According to the structure and characteristics of a three-phase cascaded H-bridge (CHB) of a high-power multilevel converter, the problem of DC side voltage imbalance in practical applications and the disadvantage where the complexity of the traditional centralized control voltage equalization scheme increases rapidly with an increase of the number of modules both need to be solved. In addition, with the characteristic that distributed control is conducive to the expansion of the system to high-power and multi-module cascade, a new quasi-distributed equalization control strategy is proposed in this paper. The new equalization control strategy combines the traditional closed-loop control with the modulation ratio correction method. On the basis of the traditional closed-loop control, an equalization control module is added to realize a balanced output of the DC side voltage. The control of the equalization control module is simple and flexible, and the complexity of the overall control algorithm is independent of the number of modules. Finally, the correctness and reliability of the control method are verified by experiments.
Zipeng Gong,Ying Chen,Ruijie Zhang,Qing Yang,Yajie Wang,Yan Guo,Bingbing Zhou,Xiaogang Weng,Xuchen Liu,Yujie Li,Xiaoxin Zhu,Yu Dong 대한약학회 2015 Archives of Pharmacal Research Vol.38 No.10
Berberine is one of active alkaloids from Rhizomacoptidis in traditional Chinese medicine. The pharmacokineticsof berberine in rat plasma were compared betweennormal and chronic visceral hypersensitivity irritable bowelsyndrome rats (CVH-IBS) established by mechanical colonirritation using angioplasty balloons for 2 weeks after oraladministration of berberine hydrochloride (25 mg/kg) withthe equivalent dose of 22 mg/kg for berberine according tobody weight. Immunohistochemical analysis of c-fos andmyosin light chain kinase (MLCK) and immunofluorescenceanalysis of MLCK in rat colon were conducted. Quantificationof berberine in rat plasma was achieved by using a sensitiveand rapidUPLC-MS/MSmethod. Plasma samples werecollected at 15 different points in time and the pharmacokineticparameters were analyzed by WinNonlin software. Thegreat different pharmacokinetic behavior of berberine wasobserved between normal and CVH-IBS model rats. Compared with normal group, T1/2 and AUC(0–t) of berberinein the model group were significantly increased, respectively(573.21 ± 127.53 vs 948.22 ± 388.57 min; 8,657.19 ±1,562.54 vs 11,415.12 ± 1,670.72 min.ng/ml). Cl/F of berberinein the model group significantly decreased, respectively(13.89 ± 1.69 vs 9.19 ± 2.91 L/h/kg). Additionally,the expressions of c-fos and MLCK in model group werehigher than those in normal group. The pharmacokinetic behaviorof berberine was significantly altered in CVH-IBSpathological conditions, which indicated the dosage modificationof berberine hydrochloride in CVH-IBS were necessary. Especially, improved exposure to berberine in ratplasma inCVH-IBSmodel rats was attributed to increased theexpression of MLCK.
Ratcheting behavior of pressurized Z2CND18.12N stainless steel pipe under different control modes
Xu Chen,Xiaohui Chen,Gang Chen,Duomin Li 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.18 No.1
With a quasi-three point bending apparatus, ratcheting deformation is studied experimentally on a pressurized austenitic stainless steel Z2CND18.12N pipe under bending load and vertical displacement control, respectively. The characteristic of ratcheting behavior of straight pipe under both control methods is achieved and compared. The cyclic bending loading and internal pressure influence ratcheting behavior of pressurized straight pipe significantly under loading control and the ratcheting characteristics are also highly associated with the cyclic displacement and internal pressure under displacement control. They all affect not only the saturation of the ratcheting strain but the ratcheting strain rate. In addition, ratcheting simulation is performed by elastic.plastic finite element analysis with ANSYS in which the bilinear model, Chaboche model, Ohno.Wang model and modified Ohno-Wang model are applied. By comparison with the experimental data, it is found that the CJK model gives reasonable simulation. Ratcheting boundaries under two control modes are almost same.
Xu Chen,Chun’an Tang,Xiangyong Kong 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.5
The deep-buried rock may experience external disturbance loads and bear overstress simultaneously in the process of free surface formation of excavation. However, the mechanical behaviors and responses under these complex stress conditions are still poorly understood. The main purpose of this paper focuses on investigating effect of frequency and amplitude of external disturbance load on stress-strain behaviors of rock samples, progressive damage evolution and failure characteristics. Using a newly developed triaxial test system at Huaqiao University a series of disturbance tests with different frequencies (5 Hz, 10 Hz, and 20 Hz) and different amplitudes (1.0 MPa, 2.5 MPa, and 5.0 MPa) was carried out on sandstone samples at the axial stress level of 85% of uniaxial compressive strength. According to the experimental results, the frequency and amplitude of the axial disturbance stress have important effects on time duration until failure, and the changing trends of axial and radial strain versus time in disturbance loading phase are extremely similar with regime I and regime II—transient creep and steady-state creep—in idealized one-dimensional creep curve. Furthermore, damage variable defined in terms of residual strain method can well reflect the gradual increase in damage degree of rock samples in disturbance loading tests under different disturbance frequencies and different amplitudes conditions. The fragmentation degree and ductility characteristics of the failure of rock sample gradually increase with the disturbance frequency and amplitude.
Evolution of Microstructures and Properties in AlxCrFeMn0.8Ni2.1 HEAs
Xu Chen,Di Gao,Jia Xuan Hu,Ye Liu,Chang Ping Tang 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.5
The microstructures, compression and corrosion behaviors of the as-cast AlxCrFeMn0.8Ni2.1high-entropy alloys (0 ≤ x ≤ 2.3)were investigated in this paper. It was found that the crystal structure changed from initial dual FCC structure to mixed FCCand BCC structure, then to BCC structure as the increasing of Al content. Al0.8CrFeMn0.8Ni2.1alloy exhibited a typicalspinodal structure consisting of alternating two phases microstructure. Moreover, sunflower-like microstructure was obtainedin the as-cast AlxCrFeMn0.8Ni2.1alloys (1.0 ≤ x ≤ 2.0). With the increasing of Al, the macrohardness increased while the plasticitydecreased in the alloys. The addition of an appropriate amount of Al could improve the compressive fracture strengthof the alloys. In addition, the corrosion resistance deteriorated slightly with the increasing of Al in 1 mol/L NaCl solution.
Xu Chen,Jing-Lei Zhao,Gui-Lin She,Yan Jing,Hua-Yan Pu,Jun Luo 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.5
Fluid-conveying tubes are widely used to transport oil and natural gas in industries. As an advanced composite material, functionally graded carbon nanotube-reinforced composites (FG-CNTRC) have great potential to empower the industry. However, nonlinear free vibration of the FG-CNTRC fluid-conveying pipe has not been attempted in thermal environment. In this paper, the nonlinear free vibration characteristic of functionally graded nanocomposite fluid-conveying pipe reinforced by single-walled carbon nanotubes (SWNTs) in thermal environment is investigated. The SWCNTs gradient distributed in the thickness direction of the pipe forms different reinforcement patterns. The material properties of the FGCNTRC are estimated by rule of mixture. A higher-order shear deformation theory and Hamilton’s variational principle are employed to derive the motion equations incorporating the thermal and fluid effects. A two-step perturbation method is implemented to obtain the closed-form asymptotic solutions for these nonlinear partial differential equations. The nonlinear frequencies under several reinforcement patterns are presented and discussed. We conduct a series of studies aimed at revealing the effects of the flow velocity, the environment temperature, the inner-outer diameter ratio, and the carbon nanotube volume fraction on the nature frequency.