The impact of multi‐group multi‐layer network structure on the performance of distributed consensus building strategies

We consider a structural approach to the consensus building problem in multi‐group multi‐layer (MGML) distributed sensor networks (DSNs) common in many natural and engineering applications. From among the possible network structures, we focus on bipartite graph structure as it represents a typical MGML structure and has a wide applicability in the real world. We establish exact conditions for consensus and derive a precise relationship between the consensus value and the degree distribution of nodes in a bipartite MGML DSN. We also demonstrate that for subclasses of connectivity patterns, convergence time and simple characteristics of network topology can be captured by explicit algebra. Direct inference of the convergence behavior of consensus strategies from MGML DSN structure is the main contribution of this paper. The insights gained from our analysis facilitate the design and development of large‐scale DSNs that meet specific performance criteria. Copyright © 2012 John Wiley & Sons, Ltd.     

A lossless image compression algorithm using variable block sizesegmentation

The redundancy in digital image representation can be classified into two categories: local and global. In this paper, we present an analysis of two image characteristics that give rise to local and global redundancy in image representation. Based on this study, we propose a lossless image compression scheme that exploits redundancy both at local and global levels in order to obtain maximum compression efficiency. The proposed algorithm segments the image into variable size blocks and encodes them depending on the characteristics exhibited by the pixels within the block. The proposed algorithm is implemented in software and its performance is better than other lossless compression schemes such as the Huffman, the arithmetic, the Lempel-Ziv and the JPEG.     

A Servo-Control System Using a Self-Controlled Synchronous Motor (SCSM) with Sliding Mode Controller

The application of sliding mode control for improving the dynamic response of a self-controlled synchronous motor (SCSM) based position servo system is presented. Sliding mode control gives fast dynamic response with no overshoot and zero steady-state error. It has the important feature of being highly robust, i.e., insensitive to plant parameter variations and external disturbances. A design procedure is outlined for the sliding mode controller for a servo driving using the self-controlled synchronous motor. A novel scheme for fast torque reversal is proposed and implemented. Digital computer simulation of the overall position control system is carried out using a time domain model in the d-q reference frame. The rigorous simulation of the servo system with sliding mode control shows the existence of limit cycles in the position response with certain type of speed encoder. Experimental results are provided for a 3-hp synchronous motor based servo drive. The sliding mode controller is implemented using a single-board microcomputer which controls a GTO thyristor current source inverter to drive the motor.     

An Auxiliary Current Impulse Commutated Inverter with Least Trapped Energy: Analysis and Optimization

ABSTRACT

This paper presents the operation, analysis and optimization of an auxiliary current impulse commutated inverter that has least or no trapped energy. The operation of the inverter is described and its salient features are discussed in relation to the modified McMurray Inverter which is the most commonly used inverter. The trapped energy in the commutation circuit is studied and is shown to be the least compared to that in modified McMurray Inverter. The optimum operating parameters are derived analytically. The advantages of this inverter in pulse-width-modulated (PWM) inverter applications are examined. Prototype unit of this inverter has been built, tested and experimental results are presented.     

Optimal Pulsewidth Modulation for Current Source Inverters

Two different pulsewidth modulation (PWM) schemes for current source inverters (CSI) are described. The first one is based on off-line optimization of individual switching angles and requires a microprocessor for implementation and the second one uses a special subharmonic modulation and could be implemented with analog and medium-scale integration (MSI) digital circuits. When CSI's are used in ac motor drives, the optimal PWM pattern depends on the performance criteria being used, which in turn depend on the drive application. In this paper four different performance criteria are considered: 1) current or torque harmonic elimination, 2) current harmonic minimization, 3) speed ripple minimization, and 4) position error minimization. As an example a self-controlled synchronous motor (SCSM) supplied by the PWM CSI is considered. The performance of the CSI-SCSM with the optimal PWM schemes proposed herein are compared with that using a conventional 120° quasi-square wave current.     

Controller-induced parasitic torque ripples in a PM synchronous motor

Permanent magnet (PM) synchronous machines with a sinusoidal back electromotive force are ideally capable of torque-ripple-free operation. However, parasitic torque ripples can still be induced from motor design and controller implementation. This paper focuses on a systematic analysis of possible sources of torque ripple in a PM synchronous machine drive resulting from limitations in the motor controller. It takes into account the effects of finite encoder resolution, controller CPU word length, current sensing errors, and inverter pulsewidth-modulation switching. Approaches for analyzing and calculating torque ripple from each of those sources have been developed. Characteristics of the various parasitic torque ripples are discussed. Experimental and simulation data to verify important results are also presented.