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Convexification of hybrid AC-DC Optimal Power Flow with Line-Commutated Converters

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CSEE Journal of Power and Energy Systems 2024年第2期10卷 617-628页

作者： hongyuan Liang Zhigang Li J.h.Zheng q.h.Wu School of Electric Power Engineering South China University of TechnologyGuangzhou 510641China

Line-commutated converter (LCC)-based high-voltage DC (hVDC) systems have been integrated with bulk AC power grids for interregional transmission of renewable power. The nonlinear LCC model brings additional nonconvexity to optimal power flow (OPF) of hybrid AC-DC power grids. A convexification method for the LCC station model could address such nonconvexity but has rarely been discussed. We devise an equivalent reformulation for classical LCC station models that facilitates second-order cone convex relaxation for the OPF of LCC-based AC-DC power grids. We also propose sufficient conditions for exactness of convex relaxation with its proof. Equivalence of the proposed LCC station models and properties, exactness, and effectiveness of convex relaxation are verified using four numerical simulations. Simulation results demonstrate a globally optimal solution of the original OPF can be efficiently obtained from relaxed model.

关键词： AC-DC power system convex relaxation linecommutated converter optimal power flow second-order cone programming

Solid-State Interfacial reaction between Eutectic Au-Ge Solder and Cu/Ni(P)/Au Metalized Ceramic Substrate and Its Suppression

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Journal of Materials Science & Technology 2015年第5期31卷 445-452页

作者： F.q.Lang h.Yamaguchi h.Nakagawa h.Sato Advanced Power Electronics research Center(ADPErC) National Institute of Advanced Industrial Science and Technology(AIST).Central 21-1-1UmezonoTsukubaIbaraki 305-8568.Japan

Eutectic Au-12 Ge solder was employed to bond the SiC power devices to a Si3N4/Cu/Ni（P）/Au multilayered *** high-temperature reliability of the bond was investigated in detail at 200,250,300 and 330 ℃,*** and Ni5Ge3intermetallic compounds（IMCs） were identified at the Au-12Ge/Ni（P） interface by micro X-ray diffraction（μXrD） and scanning electron microscopy（SEM）equipped with energy dispersive X-ray analysis（EDX）.The growth of the Ni-Ge IMCs was dominated by Ni5Ge3layer,which formed at the Ni5Ge3/NiGe interface by outward diffusion of Ni from the Ni（P） *** activation energy of the total Ni-Ge IMCs growth was 66 kJ/*** shear strength of the bond was tested at both 25 ℃ and the aging temperatures,*** shear strength decreased slightly after aging at 200 and 250 ℃.The shear strength tested at 250 ℃ was 46 MPa after aging at 250 ℃ for 3000 *** shear strength aged at 300 and 330 ℃ rapidly decreased with aging time due to the rapid growth of the *** slow down the interfacial reaction between the high temperature solder and the Ni（P）layer,an approximately 200 nm-thick Ta/TaN/Ta new diffusion barrier（DB） was deposited on the *** by transmission electron microscopy（TEM） equipped with EDX,reveals that the Ta/TaN/Ta DB was bonded well to the Ni（P） layer and the *** temperature storage test at 330 ℃ for1500 h reveals that the bond of the SiC devices maintained its high shear strength of approximately56 MPa without *** new DB effectively suppressed the interfacial reaction between the Au-12 Ge solder and the Ni（P） layer of the substrate.

关键词： high-temperature solder Interfacial reaction Activ

Dispatchable region for Active Distribution Networks Using Approximate Second-order Cone relaxation

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CSEE Journal of Power and Energy Systems 2023年第6期9卷 1999-2007页

作者： Zhigang Li Wenjing huang J.h.Zheng q.h.Wu School of Electric Power Engineering South China University of TechnologyGuangzhou 510640China

Uncertainty in distributed renewable generation threatens the security of power distribution *** concept of dispatchable region is developed to assess the ability of power systems to accommodate renewable generation at a given operating *** DC and linearized AC power flow equations are typically used to model dispatchable regions for transmission systems,these equations are rarely suitable for distribution *** achieve a suitable trade-off between accuracy and efficiency,this paper proposes a dispatchable region formulation for distribution networks using tight convex *** cone relaxation is adopted to reformulate AC power flow equations,which are then approximated by a polyhedron to improve ***,an efficient adaptive constraint generation algorithm is employed to construct the proposed dispatchable *** studies on distribution systems of various scales validate the computational efficiency and accuracy of the proposed method.

关键词： Dispatchable region distribution system renewable power generation second-order cone relaxation uncertainty

Comparing Ordinary Kriging and regression Kriging for Soil Properties in Contrasting Landscapes

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Pedosphere 2010年第5期20卷 594-606页

作者： q.ZhU h.S.LIN Department of Crop and Soil Sciences 116 ASI BuildingThe Pennsylvania State UniversityUniversity ParkPA 16802(USA)

The accuracy between ordinary kriging and regression kriging was compared based on the combined consideration of sample size,spatial structure,and auxiliary variables(terrain indices and electromagnetic induction surveys) for a variety of soil properties in two contrasting landscapes(agricultural ***).When spatial structure could not be well captured by point-based observations(e.g.,when the ratio of sample spacing over correlation range was > 0.5),or when a strong relationship existed between target soil properties and auxiliary variables(e.g.,their r2 was > 0.6),regression kriging(rK) was more accurate for interpolating soil properties in both landscapes ***,ordinary kriging(OK) was *** depth and wetness condition did not appear to affect the selection of kriging for soil moisture interpolation,because they did not significantly change the ratio of sample spacing over correlation range and the relationship with the auxiliary *** of a smaller ratio of elevation change over total study area(E/A = 1.2) and multiple parent materials in the agricultural land,OK was generally more accurate in that *** contrast,a larger E/A ratio of 6.8 and a single parent material led to rK being preferable in the steep-sloped forested *** results from this study can be useful for selecting kriging for various soil properties and landscapes.

关键词： geostatistics soil moisture spatial interpolation spatial structure

MATrIX INVESTIGATION ON ISAIChEV OrIENTATION rELATIONShIP

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Acta Metallurgica Sinica(English Letters) 1999年第2期12卷 185-190页

作者： Sheng, Z.q. Xiao, h. Nuclear Power Inst of China Chengdu China

By means of TEM technique the orientation relationships of cementite, precipitated from islands of granular bainite during tempering, with ferrite have been observed. By calculating the eigenvalues and eigenvectors of transformation matrix, Isaichev relationship has been analyzed. The results indicate that Isaichev relationship is indeed the sum of Kurdjumov-Sachs relationship and Pitsch relationship, so the viewpoint that the cementite with Isaichev relationship precipitates from austenite, instead of ferrite, was confirmed. Moreover, the matrix calculation shows that three reported orientation relationships among austenite, ferrite and cementite in pearlitic transformation cannot be simultaneously valid. (Edited author abstract) 4 refs.

关键词： Carbides Crystal orientation Eigenvalues and eigenfunctions Nuclear reactors Pearlitic transformations Phase transitions

Effect of Base Material on Microstructure and Texture Evolution of a Ti–6Al–4V Electron-Beam Welded Joint

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Acta Metallurgica Sinica(English Letters) 2017年第5期30卷 499-504页

作者： G.q.Wang Z.B.Zhao B.B.Yu J.r.Liu q.J.Wang J.h.Zhang r.Yang J.W.Li School of Materials Science and Engineering University of Science and Technology of China Institute of Metal research Chinese Academy of Sciences Science and Technology on Power Beam Processes Laboratory Beijing Aeronautical Manufacturing Technology Research Institute

The effect of base material（BM） on microstructure and crystallographic orientation evolution of a Ti–6Al–4V electron-beam welded joint was investigated. Meanwhile, the crystallographic orientation of prior b grains was studied by advanced electron backscattered diffraction data processing. The inhomogeneity of microstructure within welded joint was formed due to the different microstructures of BM. By comparing microstructure details of the welded joint, including microstructure morphology and crystallographic orientation with those of the base material, it can be found that both the microstructure morphology and crystallographic orientation of the EBW joint would be controlled by BM.

关键词： Electron-beam welding Titanium alloys Prior b orientation Microstructure Texture

Curvature-induced noncommutativity of two different components of momentum for a particle on a hypersurface

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Communications in Theoretical Physics 2021年第2期73卷 73-77页

作者： Z Li X Yang q h Liu School for Theoretical Physics School of Physics and ElectronicsHunan UniversiyChangsha 410082China School of Materials Science and Engineering Guilin University of Electronic TechnologyGuilin541004China Synergetice Innovation Center for quantum Efects and Applications(SICqEA) Hunan Normal UniversityChangsha 410081China

As a nonrelativistic particle constrained to remain on an(N−1)-dimensional((N≥2))hypersurface embedded in an N-dimensional Euclidean space,two different components pi and pj(i,j=1,2,3,...N)of the Cartesian momentum of the particle are not mutually commutative,and explicitly commutation relations[p^(^)_(i),p^(^)_(j)](≠0) depend on products of positions and momenta in uncontrollable *** generalized Dupin indicatrix of the hypersurface,a local analysis technique,is utilized to explore the dependence of the noncommutativity on the curvatures around a local point of the *** first finding is that the noncommutativity can be grouped into two categories;one is the product of a sectional curvature and the angular momentum,and another is the product of a principal curvature and the *** second finding is that,for a small circle lying a tangential plane covering the local point,the noncommutativity leads to a rotation operator and the amount of the rotation is an angle anholonomy;and along each of the normal sectional curves centering the given point the noncommutativity leads to a translation plus an additional rotation and the amount of the rotation is one half of the tangential angle change of the arc.

关键词： constrained motion quantization hypersurface Dirac brackets geometric momentum

NUMErICAL SIMULATION OF TEMPErATUrE FIELD DUrING MAGNETIC FIELD qUENChING

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Acta Metallurgica Sinica(English Letters) 2005年第6期18卷 773-776页

作者： M. h. Liu Z.h. Li X.q. Yu J.r. Chen Kunming University of Science ＆ Technology Kunming 650093 China hebei University of Science ＆ Technology Shijiazhuang 050018 China

Based on the theories of the heat transfer, the principle of phase transformation and the theory of electric and magnetic field, the mathematical model of transient temperature field involving phase transformation during magnetic field quenching is established. The heat exchange equation including magnetic field is founded. The finite element equation is set up. The distributing of transient temperature on the coupling effects of heat and magnetism is obtained. With test and measurement, the results show that after magnetic field quenching, cooling velocity is decreased, cooling curve is flatten out, and the hardness is slightly raised.

关键词： magnetic field quenching specific heals abrupt change non-linear heatconduction equation finite element equation

Cascaded Sliding-mode Observer and Its Applications in Output Feedback Control Part I:Observer Design and Stability Analysis

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CSEE Journal of Power and Energy Systems 2021年第2期7卷 295-306页

作者： Tianhao Wen Yang Liu q.h.Wu Luonan qiu School of Electric Power Engineering South China University of TechnologyGuangzhou 510640China

This paper proposes a cascaded sliding-mode observer for systems with high relative degree and studies its applications in output feedback controller *** part I,the working principle and parameter design of the proposed observer are discussed in *** is proved that,within a sufficiently short period of time,the states of the proposed observer will reach the intersection of all the sliding *** sliding surfaces,the observation error of the proposed observer will converge to sufficiently small *** with traditional high-gain observers,the proposed observer has smaller gain *** addition,the peaking-phenomenon occurred in the proposed observer is less ***,the proposed observer has a convergence rate of observation error as fast as that of traditional high-gain *** studies are carried out on a fifth-order system to verify the properties of the proposed observer.

关键词： Sliding-mode observer stability output feedback control