N. Ammasai Gounden

A Single-Sensor-Based MPPT Controller for Wind-Driven Induction Generators Supplying DC Microgrid

In this paper, a simple method of tracking the maximum power (MP) available in the wind energy conversion system (WECS) for dc microgrid application is proposed. A three-phase diode bridge rectifier along with a dc-dc converter has been employed between the terminals of a wind-driven induction generator and dc microgrid. Induction generator is being operated in self-excited mode with excitation capacitor at stator. The output current of the dc-dc converter, i.e., dc-grid current is considered as a control variable to track the MP in the proposed WECS. Thus, the proposed algorithm for maximum power point tracking (MPPT) is independent of the machine and wind-turbine parameters. This algorithm has been implemented using dsPIC30F4011 controller. Furthermore, a method has been developed for determining the duty ratio of the dc-dc converter for operating the proposed system in MPPT condition using wind-turbine characteristics, steady-state equivalent circuit of a induction generator, and power balance in power converters. Circuit simplicity and simple control algorithm are the major advantages of the proposed configuration for supplying power to the dc microgrid from the proposed small-scale WECS. The successful working of the proposed algorithm for MPPT has been demonstrated with extensive experimental results along with the simulated values.

SEMALRU: An Implementation of modified web cache replacement algorithm

The increasing demand for World Wide Web (WWW) services has made document caching a necessity to decrease download times and reduce Internet traffic. This work aims at implementing SEMALRU- A Semantic and Least Recently Used Web cache replacement policy. The basic LRU replacement policy is augmented with Semantic content of web pages to improve the efficiency of the replacement algorithms in terms of Hit Rate and Byte Hit Rate and to minimize the number of replacements made in cache. There are many well-known cache replacement policies based on size, recency, and frequency. This new improvised replacement policy attempts to implement cache replacement based on two parameters namely the semantics of the contents of web pages and the time of last access of the document. SEMALRU evicts documents that are less related to an incoming document or least recently used document which needs to be stored in the cache. This makes sure that only related documents are stored in the cache; hence the contents of the cache represent the documents of interest to the user and then ranked by recency. This policy tunes the performance of the existing replacement algorithms through analyzing the semantic content of the document and the recency of the document. A detailed algorithm to identify unrelated documents and documents that are least recently used has been devised. The policy was tested in a simulated environment with the related and unrelated set of user access pattern. . The parameters pertinent to cache replacement algorithms are computed and the results showing the improvement in the efficiency of the algorithm are furnished.

A chaos based image encryption and lossless compression algorithm using hash table and Chinese Remainder Theorem

No useful information is leaked out as full encryption is done.A very larger key space of 10195 is achieved.Complex diffusion matrix provides strong sensitivity.A lossless compression ratio of 5:1 is achieved. A chaos based image encryption and lossless compression algorithm using hash table and Chinese Remainder Theorem is proposed. Initially, the Henon map is used to generate the scrambled blocks of the input image. The scrambled block undergoes a fixed number of iterations based on the plain image using Arnold cat map. Since hyper chaos system has complex dynamical characteristics than chaos, the confused image is further permuted using the index sequence generated by the hyper chaos along with hash table structure. The permuted image is divided into blocks and the diffusion is carried out either by using Lorenz equations or by using another complex matrix generated from the plain image appropriately. Along with diffusion, compression is also carried out by Chinese Remainder Theorem for each block. This encryption algorithm has high key space, good NPCR and UACI values and very less correlation among adjacent pixels. Simulation results show the high effectiveness and security features of the proposed algorithm.

Development of BLDC Motor-Based Elevator System Suitable for DC Microgrid

In recent days, utilization of the renewable energy sources has been emphasized in high-rise buildings, where dc microgrid is established. It is known that the brushless direct current (BLDC) motors have smooth speed control, high-power density, and less complexities in power converter and controller when operated with dc supply as compared to other electrical motors. Hence, this paper enunciates the scope of using BLDC motors for elevator systems suitable for operating with a dc microgrid. For analyzing the proposed BLDC motor-based elevator system, a MATLAB mechatronic simulation model has been developed by inserting various electrical and mechanical components. Four quadrant operation of the proposed elevator system has also been indicated with the simulation results. To demonstrate the successful working of the proposal, a prototype elevator system has been designed and developed in the laboratory. The overall closed-loop controller has been implemented using a Xilinx Spartan-3E field programmable gate array (FPGA). Experiments have been conducted for the upward and downward movement of the elevator cabin with and without load and the findings are given in this paper. Regenerative braking is also possible for the proposed system by employing a suitable gear mechanism in place of worm gear.

Investigations of an improved PV system topology using multilevel boost converter and line commutated inverter with solutions to grid issues

Abstract A photovoltaic (PV) system using multilevel boost converter (MBC) and line commutated inverter (LCI), operating in both grid-connected mode and stand-alone mode has been analysed. This proposed system extracts and feeds the maximum power to a single phase utility grid and stand-alone system simultaneously. The duty ratio of the MBC is estimated from the theoretical analysis of the proposed system, for extracting maximum power from PV array. The proposed system tracks the maximum power with the determined duty ratio which remains the same for all irradiations, for a fixed firing angle of LCI. The flexibility of supplying required proportion of extracted power to grid and stand-alone load and the elimination of a separate MPPT controller are the major benefits of the proposed system under normal grid conditions. In addition to it, the grid issues like voltage swell, blackout and brownout are considered and necessary remedial measures have been taken in the proposed system. Based on the issues, either the firing angle of LCI is adjusted or LCI is disconnected and replaced by a battery. Simulation studies have been carried out and the dynamic response of the system is observed. A laboratory prototype is built and experimental investigations have also been carried out. The theoretical analysis, simulation and experimental results are found to be closely associating with each other proving the efficacy of the proposed configuration.

Power electronic interface for grid-connected PV array using boost converter and line-commutated inverter with MPPT

Many methods for interfacing PV system with utility grid have been reported in the literature. In this paper, a power electronic interface using boost converter and line commutated inverter is proposed with maximum power point tracking (MPPT), for the first time. This paper presents the design, simulation and implementation of a simple power electronic interface for grid connected PV array using boost converter and line commutated inverter. The controller extracts maximum power from the solar array and feeds it to the single-phase utility grid. A closed loop scheme employing a PI controller has been modeled in the power system blockset platform and the complete system has been simulated. A prototype of the proposed system is built in the laboratory and simulated results are experimentally verified.

A microcontroller based power electronic controller for PV assisted DC motor control

A PIC microcontroller based closed loop speed control scheme has been developed for the speed control of a separately excited DC motor fed from PV array. An IGBT based boost converter is used as an interface between PV array and the DC motor. The microcontroller has been programmed to automatically vary the duty cycle of the boost converter depending upon the set/required speed of the motor. The DC motor model has been developed and the complete simulink model of the proposed scheme has been built using MATLAB/PSB. Simulation studies and experimental investigations have been carried out on a laboratory size prototype separately excited DC motor fed from a PV array and the results are presented. The comparison of experimental and simulation results shows very close agreement between the two thus validating the controller proposed.

Simulation of Photovoltaic Array-driven Electric Machines with Power Electronic Interfaces

Power electronic interfaces between photovoltaic (PV) arrays and electric machines are necessary in order to match the drive characteristics with the characteristics of the array for efficient utilization of the resource. This paper proposes a model for the simulation of a complete solar PV power electronic conversion system in circuit simulation software, where a model of a PV array is not readily available in their libraries. The proposed circuit-based PV model is employed to simulate the waveforms of a direct current (DC) motor and induction motor drive system fed by a chopper and inverter, respectively. Close resemblance between experimental and simulated waveforms is established to validate the simulation. A quasi-stationary approach for simulating the dynamics of a PV-fed drive with temperature and irradiation variation has also been implemented in the simulation model. The details of the design of a fuzzy controller based on the simulation and its validation are also presented in this paper.Power electronic interfaces between photovoltaic (PV) arrays and electric machines are necessary in order to match the drive characteristics with the characteristics of the array for efficient utilization of the resource. This paper proposes a model for the simulation of a complete solar PV power electronic conversion system in circuit simulation software, where a model of a PV array is not readily available in their libraries. The proposed circuit-based PV model is employed to simulate the waveforms of a direct current (DC) motor and induction motor drive system fed by a chopper and inverter, respectively. Close resemblance between experimental and simulated waveforms is established to validate the simulation. A quasi-stationary approach for simulating the dynamics of a PV-fed drive with temperature and irradiation variation has also been implemented in the simulation model. The details of the design of a fuzzy controller based on the simulation and its validation are also presented in this paper.

Analysis and Control of Wind-Driven Stand-Alone Doubly-Fed Induction Generator with Reactive Power Support from Stator and Rotor Side

Hybrid-excited system has been formulated for the operation of wind-driven Doubly-Fed Induction Generators (DFIGs) for stand-alone power supplies. Here, apart from the rotor side excitation of DFIG employing SPWM inverter supplied through set of batteries, the generator is partially excited by fixed capacitor at the stator terminals. The steady-state equivalent circuit and its analysis for the proposed system have been devised and presented. The selection of stator capacitor has clearly been brought out. An attempt is also made for sizing of various components such as inverter and battery for the given machine rating and other operating conditions. Phasor diagram representation of the proposed system for typical operating conditions is also furnished. The stator voltage magnitude and frequency are maintained constant by closed loop control developed using TMS320LF2407A Digital Signal Processor (DSP) controller. Efficacy of the proposed hybrid-excited stand-alone DFIG system has been demonstrated under steady-state and dynamic operating conditions with experimental results obtained on a 3-phase, 4-pole, 415 V, 50 Hz, 5 kVA generator in the laboratory.

A unified power electronic controller for wind driven grid connected wound rotor induction generator using line commutated inverter

The implementation of a simple power converter for a wound rotor induction generator employing a three phase diode bridge rectifier and a line commutated inverter in the rotor circuit for super synchronous speeds has been proposed. The detailed working of the system in power smoothing mode and maximum power point tracking mode is presented. The current flow in the rotor circuit is controlled (by controlling the firing angle of the line commutated inverter) for controlling the stator power in both the modes. An 8 bit PIC microcontroller has been programmed to vary the firing angle of the line commutated inverter. Experiments have been carried out on a 3-phase, 3.73 kW, 400 V, 50 Hz, 4-pole, 1500 r/min wound rotor induction generator and the results obtained with the generator supplying power in both the modes are furnished. The complete scheme has been modeled using MATLAB/SIMULINK blocks and a simulation study has been conducted. The experimental waveforms are compared with the simulation results and a very close agreement between them is observed.