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Lv Pin,Zhai Yuelin,Su Xunwen,Xu Donghui,Liu Lulu,Liu Ziyang 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.6
With the increasing share of renewable energy such as wind energy in power system, flexible DC transmission technology has become an important way to effectively absorb wind energy. But the problem of synchronous sub-synchronous oscillation becomes more and more serious. To reduce the influence of sub-synchronous oscillation on interconnected systems, a Controller for energy conversion system is proposed. It is used to control the synchronous operation of the doubly-fed fan and the rectifier station to connect the doubly-fed wind farm. First, based on the impedance method, a doubly-fed wind farm and multi-module impedance model considering AC/DC dynamic coupling are established. The control energy conversion of wind power generation system, rectifier station and inverter station is designed. Second, according to Nyquist curve and impedance stability criterion, the change of system stability in the process of adjusting controller parameters is observed. Third, the system structure is simulated by MATLAB software. The effectiveness of the controller in the converter station at both ends of MMC is verified. The results show that the new controller can effectively suppress the current offset caused by SSO, and thus improve the power system stability.
Chen, Chen,Lv, Guang,Huang, Xin,Liao, Xue Pin,Zhang, Wen Hua,Shi, Bi Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.2
In this study, the homogenous Pd nanoparticles (Pd NPs) were first prepared with bayberry tannin (BT) as the stabilizers. Subsequently, the obtained bayberry tannin-stabilized Pd nanoparticles (BT-Pd) were immobilized onto ${\gamma}-Al_2O_3$ to prepare heterogeneous ${\gamma}-Al_2O_3$-BT-Pd catalysts. Fourier Transformation Infrared Spectrum (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses confirmed that the Pd NPs were well stabilized by the phenolic hydroxyl groups of BT. Transmission Electron Microscopy (TEM) observation indicated that the diameter of the Pd NPs can be effectively controlled in the range of 4.2-16.0 nm by varying the amount of BT. It is found that the ${\gamma}-Al_2O_3$-BT-Pd catalysts exhibit highly activity for various olefin hydrogenations. For example, the initial TOF (turnover frequency) of the ${\gamma}-Al_2O_3$-BT-Pd in the allyl alcohol hydrogenation is as high as $12804 mol{\cdot}mol^{-1}{\cdot}h^{-1}$. Furthermore, the ${\gamma}-Al_2O_3$-BT-Pd can be reused 5 times without significant loss of activity, exhibiting a superior reusability as compared with conventionally prepared ${\gamma}-Al_2O_3$-Pd catalysts.
Collaborative optimization of NURBS curve cross-section in a telescopic boom
Aimin Ji,Changsheng Chen,Liping Peng,Pin Lv,Xiaodi He 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.8
To improve the carrying capacity and reduce the weight of telescopic boom structure in a truck crane, a Collaborative optimization (CO) approach was applied to solve the problems of strength, stiffness and local stability in the telescopic boom structure. First, the complex optimization problem of the telescopic boom structure was decomposed into two-level optimizations: the system level and two subsystem levels for strength and local stability. Second, the underside curve of the boom’s cross-section was constructed by the Nonuniform rational B-Splines (NURBS) curve. 3D parametric solid model and the parametric finite element analysis model for the strength and the local stability were then established. Third, the mathematical models of the strength and local stability for the subsystem levels, and the system level were optimized, respectively. The adaptive relaxation factor algorithm and the penalty function approach were applied to improve the efficiency of CO. Next, the CO process which integrates the ANSYS package with ISIGHT platform was implemented. The optimal results show that the carrying capacity of the telescopic boom structure can be significantly improved and its weight efficiently is reduced. Finally, with the comparison of the stress values obtained from both the experimental test and the theoretical computation, highly coincident results could be obtained to verify the reliability of CO of a telescopic boom.
Xin Peng,Ge Baojun,Tao Dajun,Lv Pin 대한전기학회 2021 Journal of Electrical Engineering & Technology Vol.16 No.4
To research the variation characteristics and infl uence factors of air gap magnetic fi eld and electromagnetic torque of nuclear power half-speed turbine generator with stator winding inter-turn short circuit, the two-dimensional transient electromagnetic fi eld of generator-external circuit-grid coupling mathematical model is established by fi eld-circuit-network coupling method. Taking the national laboratory’s generator as an example, and comparing the simulation results of the inter-turn short circuit of the armature winding with experimental data, the correctness of the model is validated. On this basis, the simulation model of a 1407MVA nuclear power half-speed turbine generator is built. Then the stator winding inter-turn short circuit fault is simulated when the generator is connected to the grid with rated load. The characteristics of air gap fl ux density and electromagnetic torque are obtained before and after fault, as well as, the relationship between their each component and the fault degree is obtained. At the same time, the variation law of air gap fl ux density and electromagnetic torque is obtained when the relative position between fault winding and magnetic pole changes. The theoretical reference for fault diagnosis and localization using harmonic electromagnetic torque after fault is provided
Yu-lou Tian,Fang Liu,Hong-jing Sun,Pin Lv,Yu-ming Cao,Mo Yu,Yang Yue 대한치과교정학회 2015 대한치과교정학회지 Vol.45 No.5
Objective: To assess the labial and lingual alveolar bone thickness in adults with maxillary central incisors of different inclination by cone-beam computed tomography (CBCT). Methods: Ninety maxillary central incisors from 45 patients were divided into three groups based on the maxillary central incisors to palatal plane angle; lingual-inclined, normal, and labial-inclined. Reformatted CBCT images were used to measure the labial and lingual alveolar bone thickness (ABT) at intervals corresponding to every 1/10 of the root length. The sum of labial ABT and lingual ABT at the level of the root apex was used to calculate the total ABT (TABT). The number of teeth exhibiting alveolar fenestration and dehiscence in each group was also tallied. One-way analysis of variance and Tukey’s honestly significant difference test were applied for statistical analysis. Results: The labial ABT and TABT values at the root apex in the lingual-inclined group were significantly lower than in the other groups (p < 0.05). Lingual and labial ABT values were very low at the cervical level in the lingual-inclined and normal groups. There was a higher prevalence of alveolar fenestration in the lingual-inclined group. Conclusions: Lingual-inclined maxillary central incisors have less bone support at the level of the root apex and a greater frequency of alveolar bone defects than normal maxillary central incisors. The bone plate at the marginal level is also very thin.