Engineering Commons^™

Forecasting Natural Gas Demand: The Role Of Physical And Economic Factors, Ronald Brown, David Clark, George Corliss, Farrokh Nourzad, Thomas Quinn, Catherine Twetten

George F Corliss

No abstract provided.

Design And Implementation Of A Byzantine Fault Tolerance Framework For Non-Deterministic Applications, H. Zhang, Wenbing Zhao, Louise E. Moser, P. Michael Melliar-Smith

Wenbing Zhao

State-machine-based replication is an effective way to increase the availability and dependability of mission-critical applications. However, all practical applications contain some degree of non-determinism. Consequently, ensuring strong replica consistency in the presence of application non-determinism has been one of the biggest challenges in building dependable distributed systems. In this Study, the authors propose a classification of common types of application non-determinism with respect to the requirement of achieving Byzantine fault tolerance (BFT), and present the design and implementation of a BFT framework that controls these types of non-determinism in a systematic manner.

End-To-End Latency Of A Fault-Tolerant Corba Infrastructure, Wenbing Zhao, Louise E. Moser, P. Michale Melliar-Smith

Wenbing Zhao

This paper presents an evaluation of the end-to-end latency of a fault-tolerant CORBA infrastructure that we have implemented. The fault-tolerant infrastructure replicates the server applications using active, passive and semi-active replication, and maintains strong replica consistency of the server replicas. By analyses and by measurements of the running fault-tolerant infrastructure, we characterize the end-to-end latency under fault-free conditions. The main determining factor of the run-time performance of the fault-tolerant infrastructure is the Totem group communication protocol, which contributes to the end-to-end latency primarily in two ways: the delay in sending messages and the processing cost of the rotating token. To …

A Reservation-Based Extended Transaction Protocol For Coordination Of Web Services, Wenbing Zhao, Firat Kart, Louise Moser, P. Melliar-Smith

Wenbing Zhao

Web services can be used to automate business activities that span multiple enterprises over the Internet. Such business activities require a coordination protocol to reach consistent results among the participants in the business activity. In the current state of the art, either classical distributed transactions or extended transactions with compensating transactions are used. However, classical distributed transactions lock data in the databases of different enterprises for unacceptable durations or involve repeated retries, and compensating transactions can lead to inconsistencies in the databases of the different enterprises. In this article, we describe a novel reservation protocol that can be used to …

Low Loss Configuration For Integrated Pin-Schottky Limiters, Chin-Leong Lim

Chin-Leong Lim

Compared to the PIN diode limiter, the Schottky-PIN limiter improves receiver protection, but has a higher insertion loss. Low cost, plastic packaged diodes can further worsen the loss. Diode stacking, mesa diode construction, and isolating the Schottky diode with a high-impedance quarter wave line or a directional coupler can reduce loss, but detrimentally raises the limiting threshold and/or adds bulk or cost. The PIN-Schottky limiter’s insertion loss can be improved by integrating the diodes’ parasitic capacitances into a low pass ladder network, but this solution requires the PIN diode to have two anode connections. Recently, the PIN-Schottky limiter was integrated …

Design Considerations For Inertia Emulating Controllers Used In Variable Speed Wind Turbines, Lasantha Meegahapola, Amila Wickramasinghe, A P Agalgaonkar, S Perera

Dr Lasantha G Meegahapola

High penetration of wind power into power systems is likely to cause difficulties in maintaining system frequency, as in contrast to conventional synchronous generators, variable speed wind turbines (VSWTs) do not directly contribute to system inertia. To overcome this issue, it has been proposed to emulate inertia by VSWTs by extracting the kinetic energy of the turbine rotor. However, proper designing of the inertia emulating controller is essential for the optimal use of the energy potential and safe operation of the wind turbine. Some of the common controller concepts used for inertia emulation have inherent weaknesses, limiting the frequency support …

Feedback Control For Multi-Modal Optimization Using Genetic Algorithms, Jun Shi, Ole J. Mengshoel, Dipan K. Pal

Ole J Mengshoel

Estimation Of High-Dimensional Brain Connectivity From Fmri Data Using Factor Modeling, Chee-Ming Ting Phd, Abd-Krim Seghouane, Sh-Hussain Salleh, Alias M. Noor

Chee-Ming Ting

We consider identifying effective connectivity of brain networks from fMRI time series. The standard vector autoregressive (VAR) models fail to give reliable network estimates, typically involving very large number of nodes. This paper adopts a dimensionality reduction approach based on factor modeling, to enable effective and efficient high-dimensional VAR analysis of large network connectivity. We derive a subspace VAR (SVAR) model from the factor model (FM) in which the observations are driven by a lower dimensional subspace of common latent factors, following an autoregressive dynamics. We consider the principal components (PC) method which can produce consistent estimators for the FM, …

Estimating Dynamic Cortical Connectivity From Motor Imagery Eeg Using Kalman Smoother & Em Algorithm, S. Balqis Samdin, Chee-Ming Ting Phd, Sh-Hussain Salleh, Mahyar Hamedi, Alias Mohd Noor

Chee-Ming Ting

This paper considers identifying effective cortical connectivity from scalp EEG. Recent studies use time-varying multivariate autoregressive (TV-MAR) models to better describe the changing connectivity between cortical regions where the TV coefficients are estimated by Kalman filter (KF) within a state-space framework. We extend this approach by incorporating Kalman smoothing (KS) to improve the KF estimates, and the expectation-maximization (EM) algorithm to infer the unknown model parameters from EEG. We also consider solving the volume conduction problem by modeling the induced instantaneous correlations using a full noise covariate. Simulation results show the superiority of KS in tracking the coefficient changes. We …

From Verification To Implementation: A Model Translation Tool And A Pacemaker Case Study, Miroslav Pajic, Zhihao Jiang, Insup Lee, Oleg Sokolsky, Rahul Mangharam

Oleg Sokolsky

Model-Driven Design (MDD) of cyber-physical systems advocates for design procedures that start with formal modeling of the real-time system, followed by the model’s verification at an early stage. The verified model must then be translated to a more detailed model for simulation-based testing and finally translated into executable code in a physical implementation. As later stages build on the same core model, it is essential that models used earlier in the pipeline are valid approximations of the more detailed models developed downstream. The focus of this effort is on the design and development of a model translation tool, UPP2SF, and …

Model-Driven Safety Analysis Of Closed-Loop Medical Systems, Miroslav Pajic, Rahul Mangharam, Oleg Sokolsky, David Arney, Julian M. Goldman, Insup Lee

Oleg Sokolsky

In modern hospitals, patients are treated using a wide array of medical devices that are increasingly interacting with each other over the network, thus offering a perfect example of a cyber-physical system. We study the safety of a medical device system for the physiologic closed-loop control of drug infusion. The main contribution of the paper is the verification approach for the safety properties of closed-loop medical device systems. We demonstrate, using a case study, that the approach can be applied to a system of clinical importance. Our method combines simulation-based analysis of a detailed model of the system that contains …

Multi-Channel Wireless Networks With Infrastructure Support: Capacity And Delay, Hong-Ning Dai, Raymond Chi-Wing Wong, Qinglin Zhao

Hong-Ning Dai

No abstract provided.

Voltage Unbalance Emission Allocation Using Constrained Bus Voltage Method In Radial Distribution Networks, Lasantha Meegahapola, D Perera, S Perera, P Ciufo

Dr Lasantha G Meegahapola

The International Electrotechnical Committee Technical Report IEC 61000-3-13 is focused on the coordination of voltage unbalance (VU) in power systems by prescribing a methodology to determine individual VU emission allocation limits to installations. This paper provides an alternative VU emission allocation process to that of the IEC Technical Report, which is based on the concept of constrained bus voltage (CBV) method. The proposed methodology can be used in relation to radial distribution networks with symmetrical distribution lines. Several application examples of the proposed methodology are presented. It is shown that the proposed methodology is superior in comparison to the VU …

A Gradient-Based Optimum Block Adaptation Ica Technique For Interference Suppression In Highly Dynamic Communication Channels, Wasfy B. Mikhael, Tianyu Yang

Thomas Yang

The fast fixed-point independent component analysis (ICA) algorithm has been widely used in various applications because of its fast convergence and superior performance. However, in a highly dynamic environment, real-time adaptation is necessary to track the variations of the mixing matrix. In this scenario, the gradient-based online learning algorithm performs better, but its convergence is slow, and depends on a proper choice of convergence factor. This paper develops a gradient-based optimum block adaptive ICA algorithm (OBA/ICA) that combines the advantages of the two algorithms. Simulation results for telecommunication applications indicate that the resulting performance is superior under time-varying conditions, which …

Characterisation Of Gas Turbine Dynamics During Frequency Excursions In Power Networks, Lasantha Meegahapola

Dr Lasantha G Meegahapola

Gas turbines inherently depict unique frequency response characteristics compared with other conventional synchronous generation technologies as their active power output is not entirely determined by the governor response during frequency deviations of the power network. Thus, gas turbine dynamics significantly influence on system stability during frequency events in power networks. Power system and power plant operators require improved understanding of the gas turbine characteristics during various frequency events in order to mitigate adverse impact on power system. Therefore a comparative analysis has been performed between combined-cycle gas turbines (CCGTs) and open-cycle gas turbines (OCGTs) in order to characterise the dynamic …

Artifact Removal From Single-Trial Erps Using Non-Gaussian Stochastic Volatility Models And Particle Filter, Chee-Ming Ting Phd, Sh-Hussain Salleh, Z. M. Zainuddin, Arifah Bahar

Chee-Ming Ting

This paper considers improved modeling of artifactual noise for denoising of single-trial event-related potentials (ERPs) by state-space approach. Instead of the inadequate constant variance models used in existing studies, we propose to use stochastic volatility (SV) models to better describe the time-varying volatility in real ERP noise sources. We further propose a class of non-Gaussian SV models to capture the abrupt volatility changes typically present in impulsive noise, to improve artifact removal from ERPs. Two specifications are considered: (1) volatility driven by a heavy-tailed component and (2) transformation of volatility. Both result in volatility processes with heavy-tailed transition densities which …

Renewable Energy And Smart Grid Integration Through Advanced Power Electronics, Dr. Adel A. Elbaset

Dr. Adel A. Elbaset

As electricity demands are increasing day by day causing unbalance in the present grid system which results in various causes like load shedding, unbalance voltage and power quality etc which ultimately affects the consumers. Now to avoid all such situations the only option is to meet the demand by increasing generation but, we are also lagging with the conventional sources so generating more power is also not convenient by conventional ways. Therefore, recent researches are interested in renewable energy system integrated with smart grid through advanced power electronic converters. Smart gird with renewable energy sources have been regarded as the …

Optimal Design Of A Pv/Fuel Cell Hybrid Power System For The City Of Brest In France, Dr. Adel A. Elbaset

Dr. Adel A. Elbaset

This paper deals with the optimal design of a stand-alone hybrid photovoltaic and fuel cell power system without battery storage to supply the electric load demand of the city of Brest, Western Brittany in France. The proposed optimal design study is focused on economical performance and is mainly based on the loss of the power supply probability concept. The hybrid power system optimal design is based a simulation model developed using HOMER. In this context, a practical load demand profile of Brest city is used with real weather data.

Refractory Plasmonics, Urcan Guler, Alexandra Boltasseva, Vladimir M. Shalaev

U. Guler

Refractory materials are defined as those with a high melting point and chemical stability at temperatures above 2000°C. Applications based on refractory materials, usually nonmetallic, span a wide range of areas including industrial furnaces, space shuttle shields, and semiconductor technology. Metals have also been studied as refractories; however, the optical properties of those metals that have been tried for high-temperature applications were not good enough to be used in plasmonic applications (these are almost entirely based on noble metals, which are not good refractories). Refractory materials that exhibit reasonably good plasmonic behavior would undoubtedly enable new devices and boost such …

Capability Chart: A New Tool For Grid-Tied Microgrid Operation, Lasantha Meegahapola, A Jayawardena, Duane Robinson, S Perera

Dr Lasantha G Meegahapola

Increasing penetration of distributed resources have enabled the development of the microgrid concept. Similar to traditional generators, microgrids can participate in the energy market to achieve technical, economical and environmental benefits. In order to facilitate the participation in energy markets, microgrid operators need to be aware of the full capability of the microgrids. This paper presents a systematic approach for developing a capability chart for a grid-tied microgrid which represents the active and reactive power capability at the grid supply point. Capability charts have been developed for two different microgrids and the impacts of different modelling aspects have been analysed …

Wind And The Electric Grid: Transmission, Storage, And Smart Grid Options, Erik Edward Nordman, Jon Vandermolen

Erik Edward Nordman

No abstract provided.

Real-Time Beamforming Using High-Speed Fpgas At The Allen Telescope Array, William C. Barott, Oren Milgrome, Melvyn Wright, David Macmahon, Tom Kilsdonk, Peter Backus, Matt Dexter

William Barott

The Allen Telescope Array (ATA) at the Hat Creek Radio Observatory (HCRO) is a wide‐field panchromatic radio telescope currently consisting of 42 offset‐Gregorian antennas each with a 6 m aperture, with plans to expand the array to 350 antennas. Through unique back‐end hardware, the ATA performs real‐time wideband beamforming with independent subarray capabilities and customizable beam shaping. The beamformers enable science observations requiring the full gain of the array, time domain (nonintegrated) output, and interference excision or orthogonal beamsets. In this paper we report on the design of this beamformer, including architecture and experimental results. Furthermore, we address some practical …

Integration Of Upqc For Power Quality Improvement In Distributed Generation Network – A Review, Shafiuzzaman Khan Khadem, Malabika Basu, Michael Conlon

Dr. Shafiuzzaman Khan Khadem

In this paper a technical review of the integration of a Unified Power Quality Conditioner (UPQC) in a distributed generation network is presented. Although the primary task of UPQC is to minimize grid voltage and load current disturbances along with reactive and harmonic power compensation, additional functionalities such as compensation of voltage interruption and active power transfer to the load and grid have also been identified. Connection methodologies with their advantages and disadvantages are also described. Recent improvements in capacity expansion techniques and future trends for the application of UPQC in distributed modes are also identified.

A Review Of Parallel Operation Of Active Power Filters In The Distributed Generation System, Shafiuzzaman Khadem, Malabika Basu, Michael Conlon

Dr. Shafiuzzaman Khan Khadem

In this paper a technical review of parallel operation of Active Power Filter (APF) for harmonic power compensation in distributed generation (DG) network has been presented. Controlling methods and connection topologies with their pros and cons are described. Recent improvements in controlling and future trends for the application of APFs in distributed mode are also identified.

Power Quality In Grid Connected Renewable Energy Systems: Role Of Custom Power Devices, Shafiuzzaman Khan Khadem, Malabika Basu, Michael Conlon

Dr. Shafiuzzaman Khan Khadem

This paper deals with the technical review of power quality problems associated with the renewable based distributed generation systems and how the custom power devices like STATCOM, DVR and UPQC play important role in power quality improvement. IEEE and IEC standard for the grid connected renewable energy systems are one of the critical point of interest for the selection of custom power devices. Special attention has been given on the compensation of reactive power, harmonic current and voltage fluctuation during the interconnected as well as islanding mode of operation. As the solar and wind are the most abundant resources therefore …

Parallel Operation Of Inverters And Active Power Filters In Distributed Generation System: A Review, Shafiuzzaman Khan Khadem, Malabika Basu, Michael Conlon

Dr. Shafiuzzaman Khan Khadem

In this paper a technical review of parallel operation of power electronics inverters for load sharing conditions in distributed generation (DG) network is presented. Emphasis is given to parallel operation of Active Power Filters (APFs) as they are widely used to mitigate load current disturbances into DG networks. Discussions on recent advances in control strategies as applied to APFs are presented.

Power Quality Improvement Of Distributed Generation Integrated Network With Unified Power Quality Conditioner., Shafiuzzaman Khan Khadem

Dr. Shafiuzzaman Khan Khadem

With the increased penetration of small scale renewable energy sources in the electrical distribution network, maintenance or improvement of power quality has become more critical than ever where the level of voltage and current harmonics or disturbances can vary widely. For this reason, Custom Power Devices (CPDs) such as the Unified Power Quality Conditioner (UPQC) can be the most appropriate solution for enhancing the dynamic performance of the distribution network, where accurate prior knowledge may not be available. Therefore, the main objective of the present research is to investigate the (i) placement (ii) integration (iii) capacity enhancement and (iv) real …

Microgrids Of Commercial Buildings: Strategies To Manage Mode Transfer From Grid Connected To Islanded Mode, Lasantha Meegahapola, D Robinson, A Agalgaonkar, S Perera, P Ciufo

Dr Lasantha G Meegahapola

Microgrid systems located within commercial premises are becoming increasingly popular and their dynamic behavior is still uncharted territory in modern power networks. Improved understanding in design and operation is required for the electricity utility and building services design sectors. This paper evaluates the design requirements for a commercial building microgrid system to facilitate seamless mode transition considering an actual commercial building microgrid system. A dynamic simulation model of the proposed microgrid system is established (utilizing DIgSILENT Power Factory) to aid the development of planning and operational philosophy for the practical system. An economic operational criterion is developed for the microgrid …

Introduction To Electrical Engineering And The Art Of Problem Solving: Volume I, P. Frazer Williams

Peter Williams

These notes were written to accompany a two-semester introductory course in Electrical Engineering. The primary goal of the course is to introduce you to the art of technical problem solving. Conventional Electrical Engineering curricula, in favorable cases at least, produce engineers who are reasonably adept at operating many of the tools important to the field, such as mathematics and circuit analysis. Often, however, these engineers lack skill in choosing which tools to use and in designing a plan of attack to solve problems which are new to them, even though they have all the information and skills needed to fabricate …

Influence Of Photodetachment On The Switching Characteristics Of Diffuse Discharges Containing Oxygen, G. Schaefer, G. Z. Hutcheson, K. H. Schoenbach, P. F. Williams

Peter Williams

Externally sustained discharges can be used as opening and closing switches in pulsed power systems. Admixtures of attachers allow rapid opening when the external sustaining source is terminated; however, they will increase losses in the closing phase. Photodetachment has been proposed as an additional control mechanism to overcome these losses. This letter presents measurements on photoionization sustained discharges in argon and nitrogen containing admixtures of oxygen under the influence of laser radiation. Strong changes of the voltage-current characteristics have been observed. The influence of parameters such as percentage of O2, laser power, laser pulse width, and circuit impedance is presented. …