DSP based inverter control for alternate energy systems

This paper presents a DSP based algorithm to control inverters used in interfacing alternate energy systems with the electric utility. Since a constant and ripple free dc bus voltage is not ensured at the output of alternate energy sources, the main aim of the proposed algorithm is to make the output of the inverter immune to the fluctuations in the dc input voltage. In this paper a modified space vector pulse width modulation (SVPWM) technique is proposed which will maintain the quality of the ac output of the inverter, regardless of the ripple present at the inverter input. The principle is explained qualitatively and extensive experiments have been carried out to verify and validate the proposed algorithm. A 16-bit fixed-point C2000 family DSP from Texas Instruments was used as the controller to implement the proposed control algorithm.     

Application of a stochastic modelling framework to characterize the influence of different oxide scales on the solid particle erosion behaviour of boiler grade steel

An earlier developed stochastic model has been applied to describe the relative rate of material loss from the steel surface subjected to simultaneous action of high temperature oxidation involving multiple oxides and mechanical erosion. Different oxide scale growths, namely, nickel, iron and chromium have been treated deterministically and erosion is described using a literature based probabilistic framework. Oxidation is described with a power law (parabolic) approach to quantify the rate of growth of all the three oxide scales. In consonance with the published model, erosion is treated using a probabilistic methodology as spatially random phenomena on the oxide surface. The concept of ‘erosion footprint’ has been incorporated in the present model to characterize the erosion-induced damage on the steel surface. The model has been applied to predict the relative material loss as a function of time resulted from erosion–oxidation interaction pertaining to nickel, iron and chromium oxides in dimensionless form. This investigation is expected to provide a quantitative understanding of relative material loss due to solid particle erosion for oxide scales, (composed of multiple oxides) formed on the steel components of coal-fired boilers.     

An economic design model for X¯ charts with random sampling policies

Recent literature contains many papers on the study of variable (but deterministic) sampling interval (VSI) policies for X¯ control charts. VSI policies perform better than their corresponding classical fixed-sampling-interval (FSI) policies. Results are also available in the literature for an adaptive VSI policy, an enhancement of the VSI policy, where the sample size also changes with the sampling interval. However, for many industrial (especially continuous) processes where X¯ charts are used, maintaining deterministic time intervals between samples is not possible owing to inherent randomness of the processes. In this paper we propose a new variable sampling policy, named random sampling policy (RSP), for X¯ charts in which the sampling intervals and the sample sizes (considered a function of the sampling intervals) are treated as random variables. An economic modeling framework for design of RSP with run rules is developed. Within the proposed modeling framework, special cases of RSP, such as VSI and FSI policies with and without run rules, can also be evaluated. An application of the economic model is demonstrated through design of RSP parameters for two numerical example problems.     

Natural Products Inhibit Oxidative Rancidity in Salted Cooked Ground Fish

The extent of lipid oxidation in salted cooked ground fish treated with several natural products (polyphenols, dried spices and fresh spices) was measured by the production of thiobarbituric acid reactive sub-stances (TBARS). The fresh spices, ginger and tumeric, were more potent than garlic and onion (at 10% conc) in inhibiting lipid oxidation in salted cooked ground fish. The order of antioxidative potency of the dried spices was: cloves > cinnamon > cumin ～ black pepper > fennel ～ foenugreek. The dried spices were more effective antiox-idants than fresh spices. The polyphenols were the most potent group of natural antioxidants. The order of potency of the polyphenols (0.01% concentration) was: ellagic acid > tannic acid > myricetin > quercetin.     

Diffusion-Controlled Attack of Glass Surfaces by Aqueous Solutions

Simple binary alkali oxide silica glasses and some ternary glasses derived from the binary compositions by substituting alkaline earth oxides for silica were subjected to the action of water and various aqueous solutions (pH 1.4 to 10.9) and the kinetics of the reactions were studied. In every case a root-time relation of extraction, suggesting an ion-exchange controlled diffusion mechanism, was observed, followed by a time relation of extraction. The rate and duration of diffusion depended on the pH of the solution and the reaction temperature. Above a critical pH the hydrogen ion concentration of the attacking solution was so low that the surface sites began to be occupied preferentially by alkali ions, increasing their concentration at the leached layer-solution boundary and slowing the diffusion process. For potassium glasses only, where alkali ion distribution in the leached layer was exponential, the diffusion coefficients calculated from the concentration profiles agreed well with those calculated from the extraction of potassium ions by a diffusion mechanism.     

MOISTURE SORPTION ISOTHERM, PROPERTIES OF SORBED WATER AND HEAT OF SORPTION OF SANDESH– AN INDIAN MILK PRODUCT

Moisture sorption isotherm of sandesh, one of the most popular milk products in India, was determined in terms of its moisture adsorption isotherms by gravimetrical method at 20 and 30C using various saturated salt solutions in the range of 11.2 to 97.2%. The isotherms obtained were of sigmoid shape and of the Brunauer–Emmett–Teller type. Out of three sorption models fitted to the experimental data, Caurie's model was found superior in interpreting the moisture adsorption characteristics of sandesh. The monolayer moisture content as calculated from the Caurie's model at 20 and 30C were 5.89% (dry basis [d.b.]) and 5.21% (d.b.), respectively. The values of isosteric heat of sorption as calculated from Clausius–Clapeyron equation was found to increase with decreasing moisture content at lower moisture content and approached the value of heat of vaporization of free water above 17.25% (d.b.).

PRACTICAL APPLICATIONS

The present paper describes basically the storage stability of sandesh . The sandesh is a heat–acid coagulated product of milk in Indian subcontinent and forms the part and parcel of social life, ceremonies and festivals. It has an excellent market potential and higher profit margin compared with other milk products like table butter, cheese and milk powder. Although Indian dairy industry has made rapid strides in the last few decades, there is no proper packaging system, developed so far, for storage of sandesh . Keeping pace with the growing consumers' demand for fresh, convenient and microbiologically free foods, design of proper packaging system is the need of the hour. The data presented in the paper will be very much essential for the researchers and research and development institutions for proper designing of packaging system for sandesh .     

Reduced-graphene-oxide-and-strontium-titanate-based double-layered composite: an efficient microwave-absorbing material

Microwave-absorbing materials based on reduced graphene oxide (r-GO)/strontium titanate were prepared by embedding in epoxy matrix. R-GO and strontium titanate were synthesized and characterized before composite fabrication. Microstructures of the constituent elements were studied by scanning electron microscopy and X-ray diffraction (XRD). Microwave absorption capabilities of the composite absorbers were investigated using a Vector Network Analyser in the range 8–12 GHz. A maximum reflection loss of ?7.5 and ?16.4 dB was obtained at 9.3 and 12.08 GHz, respectively, for 2% (w/w) r-GO-loaded epoxy composites. A maximum attenuation of ?12.8 dB at 9.3 GHz was obtained for the strontium titanate/epoxy composite. However, double-layer composite with r-GO/strontium titanate/epoxy composition showed the maximum reflection loss of ?15.1 dB at 9.47 GHz and ?9.65 dB at 12.3 GHz. All the results are discussed in terms of complex permeability and permittivity. The study revealed that intrinsic conductivity and polarization of the r-GO particles and dielectric polarization of the strontium titanate within epoxy matrix contribute to the microwave absorption.     

Analytical evaluation of DC capacitor RMS current and voltage ripple in neutral-point clamped inverters

The sizing of the DC-link capacitor in a three-level inverter is based on the RMS current flowing through it. This paper analyses the DC-link capacitor RMS current in a neutral-point clamped (NPC) inverter and expresses the same as a function of modulation index, line-side current amplitude and power factor. Analytical closed-form expressions are derived for the capacitor RMS current for single-phase half-bridge, single-phase full-bridge and three-phase three-leg topologies of a three-level inverter. The worst-case capacitor current stress is determined for each topology based on the analytical expressions. Further, analytical expressions are derived for the RMS values of low-frequency and high-frequency capacitor currents. These expressions are then used to estimate voltage ripple across the DC capacitor for sinusoidally modulated three-phase NPC inverter. The analytical expressions for the RMS current and voltage ripple are validated experimentally over a wide range of operating points.     

T6热处理对共晶Al-Si合金力学性能、耐磨和抗蚀性能的影响(英文)

对共晶Al-Si合金的耐磨、抗蚀性能进行研究。通过控制T6热处理参数来改变共晶Al-Si合金的组织,研究组织变化对合金的硬度、强度和拉伸性能的影响,以及对抗冲蚀和腐蚀性能的影响。采用Al-Si合金制备了一典型的农机零部件。并将Al-Si合金与常用的农机用铝材的性能进行比较。结果表明,合金的化学成分、显微组织、载荷、滑动距离和试验环境对材料的耐磨、抗冲蚀和腐蚀性能有很大的影响。铸态Al-Si合金的性能要明显优于传统的铝材,而且T6热处理能够改善Al-Si合金的性能。因此,可采用Al-Si合金来替代传统的铝材制造农机。     

Analysis of electrical explosion of wire systems for the production of nanopowder

Nanoscience and nanotechnology continue to grow as fields of scientific research and commercial development as many fundamental properties are size dependent on the nano scale. There are so many techniques for the production and characterization of various ultra fine powders. To gain a fundamental understanding of size dependant properties of matter in the nanometer size regimes and to develop nanoscale materials into useful devices to benefit society requires detailed study of the experimental methods, better methods of sample preparation of mono dispersed material in large quantities, and development of nanoparticles characterization methods. Exploding wire method is one such method for the production of metal and metal oxide nanoparticles capable of producing bulk amount of metal nanoparticles at low cost. With the intention of developing better exploding wire system for the production of nanoparticle and to understand the nanoparticle formation process, we have developed two systems in the way of optimization of the experimental set-up for final production of nanoparticles. The detail analysis of the systems and its effect on the nanoparticles has been described in the paper.