Novel direct optimal and indirect method for discretization of linear fractional systems

This paper addresses the problem of discretization of fractional differintegrators and fractional systems in general. Two new discretization schemes are proposed—optimal direct method, and computationally inexpensive indirect method. The proposed methods are highly flexible and suitable for obtaining both general purpose and specialized, application-specific approximations. Both proposed methods outperform recently proposed approximations, as it is shown in several illustrative examples.     

The derivation of the equations of moderately thick plates by the method of successive approximations

In this article the equations of a moderately thick plate are derived by the method of successive approximations. The derived equations exactly satisfy all the elastostatic equations, the plate equilibrium equations and traction free face boundary conditions.     

Design of compensation network with variable inductance for wide variation of coupling coefficient in inductive power transfer

In this paper, a design of the compensation network with a variable inductor is proposed, considering a wide variation of the coupling coefficient in the inductive power transfer (IPT). The characteristics of the proposed compensation network are analyzed with respect to the variable antenna coupling conditions. The realization of the zero voltage switching (ZVS) and the reactive power demand are discussed through the theoretical deduction and numerical simulation. Influence of the variable inductor on the compensation network characteristics is examined in detail, and the control algorithm for achieving the coupling independent constant output voltage is proposed. Detailed steps to design a prototype fulfilling all performance requirements are given. Verification of the proposed method was carried out on the experimental model. Recorded output voltage variation is within 5% over the wide coupling range, implying a quite well characteristic of the coupling independent voltage output. Experimental results match well with the calculations, validating the rightness of the proposed variable inductor tuning method.     

基于MPPMSG的混合高压直流风电系统故障穿越技术

为解决传统风电系统变换级数多的问题,文中提出了一种基于多相永磁同步电机(MPPMSG)的混合高压直流风电系统拓扑。电机多套绕组分别连接单极性变流器并在直流侧串联形成高压直接接入直流母线,一套绕组向电机注入无功功率以改善电机调速和稳态性能。岸上变电站采用电网换相换流器,直流母线短路时可阻断短路电流。为解决多绕组耦合问题,MPPMSG采用了反馈解耦的控制策略。根据发电机短路特性分析,提出了直流母线短路时限制电机短路电流以及直流故障穿越的控制策略。最后,利用PSCAD/EMTDC搭建风电系统开关电路仿真模型,验证了所提控制策略的有效性。     

Generalized charge simulation method for the calculation of the electric field in high voltage substations

This paper deals with the calculation of the electric field strength in high voltage (HV) substations comprising complex geometrical structures. Generalized charge simulation method is proposed for improving the precision of the calculation of the electric field strength. The objective of this analysis is to examine the influence of towers, HV apparatus and fences on the spatial electric field distribution. For this purpose, a three-dimensional generalized model of HV substation has been developed, including phase conductors, bypass busbars, HV apparatus, fences and towers (denoted as Full model). The obtained results of the calculation of the electric field strength are compared with the Simplified model, which only includes phase conductors connected to HV network. Verification of the proposed Full model performed by comparing the calculated and in-field measured values of the electric field strength within HV substations and in their vicinity gives very promising results.     

Polyamic acid: nanoprecipitation and electrophoretic deposition on porous supports

Polyamic acid (PAA, a precursor of polyimide) was synthesized from 4,4′-oxydiphthalic anhydride and 4,4′-oxydianiline. PAA, dissolved in dimethylsulfoxide (DMSO), was precipitated into colloidal particles after its injection into acetone. The resulting particle size distribution was found to depend on aging time of PAA solutions, their concentration, and the manner in which the solutions were mixed with acetone. PAA particles of any size down to 10 nm appeared to be achievable by decreasing the acetone/DMSO ratio. Particles in DMSO/acetone suspensions were found to have a significant negative zeta potential. Therefore, there was no need to add organic bases to form PAA anions, in contrast to all previously published studies on the PAA electrodeposition. EPD was performed onto porous stainless-steel or alumina disks, which are suitable supports (reinforcements) for membranes. The slow evaporation of DMSO residue yielded dried polymer layers, comprised of 50–100 nm PAA globules. The outer surface of layers was usually covered with a very thin, continuous PAA skin. Such supported PAA layers—after a simple imidization step via a heat treatment—could be applied as thermally resistant membranes for gas separation.     

Synthesis of DNA-Encoded Disulfide- and Thioether-Cyclized Peptides

DNA-encoded chemical library technologies enable the screening of large combinatorial libraries of chemically and structurally diverse molecules, including short cyclic peptides. A challenge in the combinatorial synthesis of cyclic peptides is the final step, the cyclization of linear peptides that typically suffers from incomplete reactions and large variability between substrates. Several efficient peptide cyclization strategies rely on the modification of thiol groups, such as the formation of disulfide or thioether bonds between cysteines. In this work, we established a strategy and reaction conditions for the efficient chemical synthesis of cyclic peptide–DNA conjugates based on linking the side chains of cysteines. We tested two different thiol-protecting groups and found that tert-butylthio (S-tBu) works best for incorporating a pair of cysteines, and we show that the DNA-linked peptides can be efficiently cyclized through disulfide and thioether bond formation. In combination with established procedures for DNA encoding, the strategy for incorporation of cysteines may be readily applied for the generation and screening of disulfide- and thioether-cyclized peptide libraries.     

Influence of salt concentration on solubility and tie-line data for the system: Formic acid + n-butanol + water

The tie-line and solubility data, i.e. formic acid (FA) + n-butanol + water + NaCl, were resolved at T = 298.15 K and under ambient pressure. The Othmer–Tobias equation was applied in this study. The experimental data were correlated and all linear correlation coefficients were found to be approximately equal to 1. Both the Universal Quasi-chemical Theory (UNIQUAC) and Nonrandom Two Liquid Theory (NRTL) and NRTL models were employed in order to compare the experimental liquid–liquid equilibrium (LLE) and tie-line data. Consequently, the calculated and experimental data proved to be a good fit. Results show that adding salt to the system proved beneficial by increasing the separation of FA from water.