A single phase photovoltaic inverter control for grid connected system

This paper presents a control scheme for single phase grid connected photovoltaic (PV) system operating under both grid connected and isolated grid mode. The control techniques include voltage and current control of grid-tie PV inverter. During grid connected mode, grid controls the amplitude and frequency of the PV inverter output voltage, and the inverter operates in a current controlled mode. The current controller for grid connected mode fulfills two requirements – namely, (i) during light load condition the excess energy generated from the PV inverter is fed to the grid and (ii) during an overload condition or in case of unfavorable atmospheric conditions the load demand is met by both PV inverter and the grid. In order to synchronize the PV inverter with the grid a dual transport delay based phase locked loop (PLL) is used. On the other hand, during isolated grid operation the PV inverter operates in voltage-controlled mode to maintain a constant amplitude and frequency of the voltage across the load. For the optimum use of the PV module, a modified P&O based maximum power point tracking (MPPT) controller is used which enables the maximum power extraction under varying irradiation and temperature conditions. The validity of the proposed system is verified through simulation as well as hardware implementation.     

Multi-switching adaptive synchronization of two fractional-order chaotic systems with different structure and different order

In this work, we combine the active and adaptive control theories, and propose a novel synchronization scheme for a class of fractional-order chaotic systems with different structure and different order. Based on the new version of fractional-order Lyapunov stability theory, we design the adaptive controllers and updating laws of different switching. We use the fractional-order Lorenz chaotic system and the fractional-order Chen chaotic system as examples to analyze the multi-switching synchronization process for fractional-order chaotic systems with different structures and different orders. Finally, numerical simulations are also given to illustrate the effectiveness and validation of the proposed method, and the model uncertainties and external disturbances are added to the considered systems to verify the robustness of the proposed controllers.     

On infinitesimal transformations and limit cycles†

A necessary condition for the existence of the limit cycle(s) of a second-order autonomous system, which can be reduced to a first-order system invariant under an infinitesimal transformation, is discussed in this paper. A method for obtaining an expression which will always include any limit cycle of the system that may exist is also shown.     

Ruthenium-containing MCM-22 and ITQ-2 as potential redox catalysts for benzhydrol oxidation

Journal of Porous Materials - About 5 wt% of ruthenium (Ru) was incorporated on layered zeolite frameworks, such as MCM-22 and ITQ-2, using the incipient wetness method. The well-dispersed...     

Electrical breakdown in very thin Al2O3 films

Electrical breakdown in very thin A1₂O₃ films of thickness less than 100 Å and sandwiched between Al and Au metal electrodes has been studied experimentally. Recovery of high resistance of the oxide insulator film has been observed (after breakdown) on the application of either a reverse voltage or a high current pulse or just by resting the junction for a few hours after the removal of the applied external voltage. An explanation for the effect is suggested. The breakdown field is found to depend on the insulator thickness, the temperature and the nature of the electrode metals. On the basis of experimental results the mechanisms for electrical break down at room temperatures and above, in very thin Al₂O₃ films, can be attributed to electronic modified thermal breakdown.     

Realizing NiO nanocrystals from a simple chemical method

Nanocrystalline NiO has been prepared successfully by a simple chemical route using NiCl₂·6H₂O and NaOH aqueous solution at a temperature of 70°C. The prepared material has been characterized from XRD, SEM, and M–H characteristics. It has been found that NiO nanocrystals have been formed which shows a superparamagnetic/superantiferromagnetic behaviour.     

Relationship between Landsat MSS data and forest tree parameters

Abstract

Band ratios, indices and radiance in the four channels of the Multi-spectral Scanner (MSS) on the Landsat-4 satellite for October 1984 and March 1985 were correlated with mean tree parameters of teak plantations (age, mean tree height, mean tree diameter at breast height, mean canopy diameter, mean canopy volume). The Landsat MSS data for March (when teak trees are leafless) were more suitable than the Landsat MSS data for October for categorizing tree parameters.     

Analysis of non-Newtonian liquids using a microfluidic capillary viscometer

We have used a self-calibrating microfabricated capillary viscometer to analyze non-Newtonian power law fluids. The capillary viscometer can generate a wide range of shear rates during a single experimental run enabling quick and accurate analysis of non-Newtonian liquids. The measurement of viscosity is based on monitoring the capillary pressure-driven movement of fluid sample whose mean velocity and, therefore, shear rate varies with time. The device has been successfully tested for accuracy and robustness with dilute as well as semidilute solutions of flexible elastic polymers including poly(ethylene oxide) and hydrolyzed polyacrylamide to an aqueous solution of a stiff rodlike polymer molecule of xanthan gum, a popular emulsifier and food thickener, as well as with ink-jet printing inks. Viscosities in the range of 1-600 cP were measured, and shear rates varying from 5 to 1000 s(-1) have been obtained on the microfabricated viscometer with the current geometry and channel dimensions. The total measurement time varied between 2 and 8 min and less than 1 microL of sample volume was required. Such a microfabricated capillary viscometer would have possible applications in quality control and manufacturing where rapid and repeated measurements need to be made using limited sample volume.     

Varna-based optimization:a novel method for capacitated controller placement problem in SDN

Recently,software defined networking(SDN)is a promising paradigm shift that decouples the control plane from the data plane.It can centrally monitor and control the network through softwarization,i.e.,controller.Multiple controllers are a necessity of current SDN based WAN.Placing multiple controllers in an optimum way is known as controller placement problem(CPP).Earlier,solutions of CPP only concentrated on propagation latency but overlooked the capacity of controllers and the dynamic load on switches,which is a significant factor in real networks.In this paper,we develop a novel optimization algorithm named varna-based optimization(VBO)and use it to solve CPP.To the best of our knowledge,this is the first attempt to minimize the total average latency of SDN along with the implementation of TLBO and Jaya algorithms to solve CPP for all twelve possible scenarios.Our experimental results show that TLBO outperforms PSO,and VBO outperforms TLBO and Jaya algorithms in all scenarios for all topologies.