A Resonant Integrator Based PLL and AC Current Controller for Single Phase Grid Connected PWM-VSI

Grid connected PWM-VSIs are being increasingly used for applications such as Distributed Generation (DG), power quality, UPS etc. Appropriate control strategies for grid synchronisation and line current regulation are required to establish such a grid interconnection and power transfer. Control of three phase VSIs is widely reported in iterature. Conventionally, dq control in Synchronous Reference Frame(SRF) is employed for both PLL and line current control where PI-controllers are used to track the DC references. Single phase systems do not have defined direct (d) and quadrature (q) axis components that are required for SRF transformation. Thus, references are AC in nature and hence usage of PI controllers cannot yield zero steady state errors. Resonant controllers have the ability to track AC references accurately. In this work, a resonant controller based single phase PLL and current control technique are being employed for tracking grid frequency and the AC current reference respectively. A single phase full bridge converter is being operated as a STATCOM for performance evaluation of the control scheme.

Erosion and cavity characteristics in rotating components

An investigation of the initiation and growth of erosion and of the effect of velocity and pressure on erosion in a rotating disk is presented. Also, the role of an intervening noncavitating period on erosion is studied. The results indicate that at high intensities the peak rate of erosion decreases with increases in pressure. The erosion rate/time curves obtained for metallic materials are explained by the eroded particle distribution and the cavity size. The average size of the eroded particles decreased when pressure and tensile strength of the material were increased. The erosion rate peaked after an intervening noncavitating period. The use of the rate of erosion, defined as an average over the entire test duration, in the equation governing the theory of erosion resulted in reasonably good correlations. The correlations reveal that it is possible to predict the length, width, and area of a cavity when the cavitation parameter σ is known. The normalized width of a cavity may be estimated if its normalized length is known.

Resonant absorption of Alfven waves and the associated phenomenon of magnetic reconnection

It is proposed that the mathematical analysis of the Alfven wave equation in inhomogeneous magnetic fields which explain the resonance absorption of Alfven surface waves near a resonant layer can also be used to show that the magnetic reconnection process can arise near the zero-frequency resonant layer driven by VLF Alfven surface waves. It is suggested that the associated phenomena of resonant absorption and magnetic reconnection can account for the recent observations of intense magnetic activity in the long-period geomagnetic micropulsation range, at cusp latitudes, during flux transfer events.

Analysis of reflection characteristics of a normal incidence plane wave on resonant sound absorbers: A finite element approach

Resonant sound absorbers are used widely as anechoic coatings in underwater applications. In this paper a finite element scheme based on the Galerkin technique is used to analyze the reflection characteristics of the resonant absorber when insonified by a normal incidence plane wave. A waveguide theory coupled with an impedance matching condition in the fluid is used to model the problem. It is shown in this paper that the fluid medium encompassing the absorber can be modeled as an elastic medium with equivalent Lamé constants. Quarter symmetry conditions within the periodic unit cell are exploited. The finite element results are compared with analytical results, and with results published elsewhere in the literature. It is shown in the process that meshing of the fluid domain can be obviated if the transmission coefficients or reflection coefficients only are desired as is often the case. Finally, some design curves for thin resonant absorbers with water closure are presented in this paper.

Synthesis and characterization of single-crystalline alpha-MoO3 nanofibers for enhanced Li-ion intercalation applications

High quality, single-crystalline alpha-MoO3 nanofibers are synthesized by rapid hydrothermal method using a polymeric nitrosyl-complex of molybdenum(II) as molybdenum source without employing catalysts, surfactants, or templates. The possible reaction pathway is decomposition and oxidation of the complex to the polymolybdate and then surface condensation on the energetically favorable 001] direction in the initially formed nuclei of solid alpha-MoO3 under hydrothermal conditions. Highly crystalline alpha-MoO3 nanofibers have grown along 001] with lengths up to several micrometres and widths ranging between 280 and 320 nm. The alpha-MoO3 nanofibers exhibit desirable electrochemical properties such as high capacity reversibility as a cathode material of a Li-ion battery.

Enhanced ionic conductivity in nano-composite solid polymer electrolyte: (PEG) (x) LiBr: y(SiO2)

In this paper, we report an enhancement in ionic conductivity in a new nano-composite solid polymer electrolyte namely, (PEG) (x) LiBr: y(SiO2). The samples were prepared, characterized, and investigated by XRD, IR, NMR, and impedance spectroscopy. Conductivity as a function of salt concentration shows a double peak. Five weight percent addition of silica nanoparticles increases the ionic conductivity by two orders of magnitude. Conductivity exhibits an Arrhenius type dependence on temperature. IR study has shown that the existence of nanoparticles in the vicinity of terminal OaEuro center dot H group results in a shift in IR absorption frequency and increase in amplitude of vibration of the terminal OaEuro center dot H group. This might lead to an enhancement in conductivity due to increased segmental motion of the polymer. Li-7 NMR spectroscopic studies also seem to support this. Thus addition of nanoparticle inert fillers still seems to be a promising technique to enhance the ionic conductivity in solid polymer electrolytes.

Global solutions describing the collapse of a spherical or cylindrical cavity

The collapse of a spherical (cylindrical) cavity in air is studied analytically. The global solution for the entire domain between the sound front, separating the undisturbed and the disturbed gas, and the vacuum front is constructed in the form of infinite series in time with coefficients depending on an ldquoappropriaterdquo similarity variable. At timet=0+, the exact planar solution for a uniformly moving cavity is assumed to hold. The global analytic solution of this initial boundary value problem is found until the collapse time (=(gamma–1)/2) for gamma le 1+(2/(1+v)), wherev=1 for cylindrical geometry, andv=2 for spherical geometry. For higher values of gamma, the solution series diverge at timet — 2(beta–1)/ (v(1+beta)+(1–beta)2) where beta=2/(gamma–1). A close agreement is found in the prediction of qualitative features of analytic solution and numerical results of Thomaset al. [1].

Non-resonant RF and microwave response: A novel technique for the characterization of superconducting materials

When examined using continuous wave electron paramagnetic resonance and nuclear magnetic resonance spectrometers, the high T-c superconductors give rise to intense, low field, 'non-resonant' absorption signals in the superconducting state. This phenomenon can be used as a highly sensitive, contactless technique for the detection and characterization of superconductivity even in samples containing only minute amounts of the superconducting phase. Further, it can also be applied to the determination of material parameters of interest such as J(c) and H-c2 in addition to being a powerful way of distinguishing between weak-link superconductivity and bulk superconductivity. The details of these aspects are discussed

Combining Bayes Classification and Point Group Symmetry under Boolean Framework for Enhanced Protein Quaternary Structure Inference

Our ability to infer the protein quaternary structure automatically from atom and lattice information is inadequate, especially for weak complexes, and heteromeric quaternary structures. Several approaches exist, but they have limited performance. Here, we present a new scheme to infer protein quaternary structure from lattice and protein information, with all-around coverage for strong, weak and very weak affinity homomeric and heteromeric complexes. The scheme combines naive Bayes classifier and point group symmetry under Boolean framework to detect quaternary structures in crystal lattice. It consistently produces >= 90% coverage across diverse benchmarking data sets, including a notably superior 95% coverage for recognition heteromeric complexes, compared with 53% on the same data set by current state-of-the-art method. The detailed study of a limited number of prediction-failed cases offers interesting insights into the intriguing nature of protein contacts in lattice. The findings have implications for accurate inference of quaternary states of proteins, especially weak affinity complexes.

Resonant absorption of alfvén waves near a neutral point

It is shown that, although the mathematical analysis of the Alfven-wave equation does not show any variation at non-zero or zero singular points, the role of surface waves in the physical mechanism of resonant absorption of Alfven waves is very different at these points. This difference becomes even greater when resistivity is taken into account. At the neutral point the zero-frequency surface waves that are symmetric surface modes of the structured neutral layer couple to the tearing mode instability of the layer. The importance of this study for the energy balance in tearing modes and the association of surface waves with driven magnetic reconnection is also pointed out.

Surface barrier effects in non-resonant microwave absorption by superconducting thin films of YBa2Cu3O7??

We present an unusual temperature dependence of hysteresis in the Lion resonant microwave absorption (NRMA) signals from superconducting thin films of YBa2Cu3O7-delta. We observe that the hysteresis increases with increase in temperature till T-c which we interpret as evidence for the presence of Bean-Livingston surface barriers (BLSB) in the single crystalline films.

Reversible Insertion of a Trivalent Cation onto MnO2 Leading to Enhanced Capacitance

Supercapacitor properties of MnO2 are studied generally in aqueous alkali metal salt solutions, often in a Na salt solution. During electrochemical discharge-charge processes, Na+ ions from the electrolyte get reversibly inserted/deinserted on the surface of MnO2 particles, which leads to redox reaction between MnOONa and MnO2. In the present study, it has been shown that MnO2 exhibits enhanced capacitance behaviour in a rare earth metal salt solution, namely, La(NO3)(3) solution in comparison with NaNO3 and Mg(NO3)(2) aqueous solutions. The specific capacitance increases with an increase in charge on the solution cation (Na+, Mg2+ and La3+). It is proposed that the number of surface sites for adsorption of cations remains unaltered in all solutions. The surface insertion of cation facilitates the reduction of Mn4+ in MnO2 to Mn3+ equivalent to the charge present on the cation. As the specific capacitance is related to the quantity of charge that is exchanged between the solid MnO2 and the aqueous solution, the trivalent cation (La3+) provides greater specific capacitance than in Mg(NO3)(2) and NaNO3 electrolytes. Accordingly, the number of Mn(IV)/Mn(III) redox pairs involved in the neighbourhood of the adsorption site is one, two and three when Na+, Mg2+ and La3+ ions, respectively, are adsorbed. (C) 2011 The Electrochemical Society. DOI: 10.1149/1.3565177] All rights reserved.