Fluorescent lamp cold starting improvement

Three approaches to improving the efficacy and startup time of commercially available cold cathode fluorescent lamps under cold ambient conditions are evaluated in this paper: heating the tube on one side; heating the tube on two sides; and heating the circumference of the outer tube. The internal power density generated by ion bombardment of the cathode and collisions in the plasma are indirectly obtained by matching simulated axial wall temperatures with those obtained by experiment at room temperature. The estimated power density is used to evaluate the temporal evolution of the axial surface wall temperature under different ambient conditions immediately after a cold start. All simulation results have been obtained using PHOENICS, a computational fluid flow program. Experiments have shown a good correlation between the time taken for the light output to reach an acceptable value and the time taken for the inner tube cold spot to reach a temperature of 0/spl deg/C. These results have been used to estimate heating time for different heater geometries and heater powers. The study shows that the conduction of heat to the outer glass envelope is the limiting process that controls the startup time. Modest improvement in startup time can be achieved by increasing heating power or by moving the heater to the side of the lamp. However, only a heater which entirely surrounds the lamp is capable of substantially decreasing the startup time.     

Power quality compensation using universal power quality conditioning system

The aim of this letter is to present a universal power quality conditioning system (UPQS) named after a unified power quality conditioner (UPQC), which is extended by adding a shunt active filter at the load side. Its main purpose is to compensate for supply voltage and load current imperfections, such as sags, swells, interruptions, imbalance, flicker, harmonics, reactive currents, and current unbalance. Converter and control analysis is presented together with results showing the UPQS modes of operation.     

Fast ferroresonance suppression of coupling capacitor voltage transformers

This paper describes a procedure for fast suppression of the phenomenon of ferroresonance in coupling capacitor voltage transformers (CCVT) without major change in the CCVT design. It is shown that it is possible to adjust parameters of the secondary overvoltage protection and the filter circuit so that the ferroresonance can be cleared in a very short time interval. The study cases reported in this paper show that ferroresonance is effectively cleared within two cycles. An implementation of metal oxide varistors (MOV) as part of passive ferroresonance protection is also addressed. The Electromagnetic Transients Program (EMTP) is used for modeling transients and fine-tuning the ferroresonance suppressing circuit. The studies are conducted on the Trench TEHMP161A CCVT.     

Modeling the base load generating units with derated states in composite power system reliability evaluation

Contents A novel approach for the construction of the equivalent two-state models for base load generating units with derated states is suggested in order to reduce the computational burden in composite power system reliability (adequacy) evaluation. The proposed equivalent is conceived in such a way to preserve the invariance of the failure probability of the generation system taken alone, under assumption that the network effects upon the generating units models are slight and can be ignored. The equivalent model suggested has been successfully tested and compared with the EFOR based model for the IEEE RT System.

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Modellierung von Grundlast Generator-Einheiten mit geschwächten Zuständen in der Berechnung der Zuverlässigkeit von elektrischen Verbundsystemen

Übersicht Ein neues Verfahren für die Zusamenfassung von den Zwei-Zustand Ersatzmodellen für die Grundlast Generator-Einheiten mit geschwächten Zustäden wird vorgeschlagen, um die Rechneranlagen-Anforderungen zu vermindern. Das entwickelte Ersatzmodell bewahrt die Invarianz der Ausfall-Wahrscheinlichkeiten des allein betrachteten Generatorsystems unter der Voraussetzung, daß der Einfluß von Übertragungs-Netzkomponenten bei Generatormodellen vernachlässigbar ist. Das vorgeschlagene Ersatmodell wird erfolgreich für das IEEE RT-System überprüft und mit dem bekannte EFOR-Modell verglichen.

     

Online control of current-source-type active rectifier usingtransfer function approach

Current-source topology AC/DC converters (buck converters) operated using pulsewidth modulation have significant drawbacks in lack of line current control and AC-side filter damping. Also, an AC-side filter is usually overrated in order to keep harmonic distortion under imposed limits. Discontinuous current at converter line inputs disables the use of current control techniques known from control of voltage-source converters. In order to overcome these problems, an online control method for the buck converter is presented in this paper. This method is based on the AC filter transfer function approach. Such an approach enables a novel solution for line-side filter optimization in the case of hysteresis line current control. This method leads to a filter with minimal apparent power (cost) and the fast and accurate converter's control response. Furthermore, a line current estimation method was developed. It uses only one current sensor at the converter DC side in order to estimate power supply currents. Suggested methods were numerically and experimentally verified     

A method for evaluating the frequency of deficiency-states ofelectric-power systems

A novel method for evaluating the frequency of deficiency-states of power systems is suggested. The method uses exact generation-capacity states and system load-duration and load-frequency characteristics. The approach accurately models load daily diagrams, including multimodal diagrams. The generating units are modeled as multistate elements. Analytic expressions for the frequency of deficiency-states are derived in closed form to avoid the accumulation of rounding errors that might appear in recursive approaches. Illustrative application examples are included     

A method for PWM rectifier line side filter optimization intransient and steady states

The purpose of this paper is to develop, design and test an overall approach to line side filter optimization for the current type PWM controlled active rectifier and to investigate influence of control system to converters performance and filter size (TkVA). For the instantly predominating offline current rectifier control methods, a line side filter optimization algorithm and corresponding computer program was proposed and developed. It uses both complete transient and steady state, characteristics of system, ensuring minimized individual and total harmonic distortion (according to standards) of line current and a good power factor together with minimum costs. Suggested method was numerically verified through the extensive simulations using SIMULINK toolbox of MATLAB software. Final verification came from the implementation on a prototype. Detailed testing was performed and the proposed algorithm showed satisfying performance under different operating conditions. As far as the authors are aware, the novel contribution coming from this paper is in completing the line side filter optimization algorithm taking into account both transient and steady state of system, power supply demands and the power factor restriction for the offline controlled current type AC/DC converter     

Application-oriented comparison of the methods for AC/DC converter harmonics analysis

Fourier transform (FT) is the most widely used tool for voltage and current waveform analysis. Nevertheless, it has certain drawbacks for time-varying signals analysis. Therefore, a need for another analysis technique appears. windowed FT, wavelet transform, and modulated lapped transform were considered in this paper. Comparison based on practical application shows the advantages of the last one. As an example, it has been applied for ac/dc converter input current harmonics analysis.     

Principles of Fusion of Inertial Navigation and Dynamic Vision

The possibility of fusion of navigation data obtained by two separate navigation systems (strap‐down inertial one and dynamic vision based one) is considered in this paper. The attention is primarily focused on principles of validation of separate estimates before their use in a combined algorithm. The inertial navigation system (INS) based on sensors of medium level quality has been analyzed on one side, while a visual navigation method is based on the analysis of a sequence of images of ground landmarks produced by an on‐board TV camera. The accuracy of INS estimations is being improved continuously by optimal estimation of a flying object's angular orientation while the visual navigation system offers discrete corrections during the intervals of presence of landmarks inside the camera's field of view. The concept is illustrated by dynamic simulation of a realistic flight scenario. © 2004 Wiley Periodicals, Inc.