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Influence of long pulse duration on time-resolved laser-induced incandescence

APPLIED PHYSICS B-LASERS AND OPTICS 2013年第3期112卷 359-367页

作者： Ditaranto, M. Meraner, C. Haugen, N. E. L. Saanum, I. SINTEF Energy Res N-7465 Trondheim Norway

Time-resolved laser-induced incandescence (LII) signal of soot in an ethylene laminar diffusion flame was measured with varying laser pulse durations in the range 50-600 ns. This study presents original results since the majority of LII studies reported are based on 7-10-ns pulse duration. The LII signal from soot is a combination of heating and cooling processes of different time scales, and the influence of the pulse duration is therefore particularly relevant. The most striking finding is that when the pulse durations is longer than approximately 100 ns, the time-resolved LII signal reveals a rebound of the LII signal during its slow decaying part. This feature occurs preferably at high fluence and is unexpected as none of the physical and chemical processes known to control LII signal behaviour, and their models suggest such an effect. The phenomenon occurs with both top hat and near Gaussian temporal laser shapes. Inspection of the time-resolved emission spectra shows no indication of a laser-induced fluorescence effect, although gas-phase PAH generated during the laser heating of soot particles cannot be rejected. Other hypotheses are that the mechanism responsible for that behaviour is linked to a slow rate change of the soot morphological characteristics or to the generation of new particles during the long-duration laser excitation. Finally, experiments show that soot volume fraction measured by integrating the temporal LII signal is not affected by the pulse duration in any regions of the flame, implying that the LII method is applicable with long pulse duration lasers.

关键词： LASER beams pulse-width modulation LAMINAR flow ETHYLENE DIFFUSION FLAME SOOT HEATING

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A torque discontinuity free new hybrid PWM approach for high speed induction motor drives

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Advances in Power Electronics 2014年第unknown期2014卷

作者： Rehman, Habibur Mahmood, Roufin Shah, Taimoor Department of Electrical Engineering School of Engineering American University of Sharjah Sharjah P.O. Box 26666 United Arab Emirates

This paper designs a hybrid speed controller in which a Sine Triangle pulse width Modulated (SPWM) inverter is used below the base speed and a square wave inverter is employed above the base speed. The two inversion techniques complement each other for their advantages and disadvantages below and above the base speed. This paper proposes a unique strategy for the transition between SPWM and square wave by simply setting the frequency of the carrier signal equal to zero. The proposed methodology in a way uses only one inversion technique and realizes a seamless transition from the SPWM to square wave compared to conventional method in which modes are simply switched from SPWM to square wave and vice versa when the speed changes above and below the base speed, respectively. Computer simulations show that the proposed technique has smoother torque transition and thus a better speed response compared to conventional approach of inverter mode switching around the base speed. The performance of proposed hybrid approach is also validated on a small prototype induction motor through experimental results. © 2014 Habibur Rehman et al.

关键词： pulse-width modulation Switching frequency Induction motor Torque Power inverter Switch

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Analytical modelling of single-phase stacked multicell multilevel converters exploiting Kapteyn (Fourier-Bessel) series

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IET POWER ELECTRONICS 2013年第6期6卷 1220-1238页

作者： Dargahi, Vahid Dargahi, Saeedeh IUST Ctr Excellence Power Syst Automat & Operat Dept Elect Engn Tehran *** Iran Univ Tabriz Fac Elect & Comp Engn Tabriz *** Iran

This study proposes a mathematical model for stacked multicell (SM) converters (SMCs), to be exploited in the analytic determination of the natural voltage balancing dynamics of the SMCs, that is, investigation of the start-up behaviour, dynamic response and natural voltage balancing phenomenon. The crux of the proposed strategy is based on the closed-form analytic solution derivation for the switching functions used in the switching of the SMCs operated under phase disposition (PD) and phase-shifted carrier (PSC) pulse-width modulation (PD-PSC-PWM) technique. Hence, the suggested approach develops an analytic solution for the Fourier series and associated Fourier coefficients pertinent to the switching functions of the SMCs by obtaining the switching instants of the PD-PSC-PWM modulator in terms of 'Kapteyn series' when the frequency of the triangular carrier waveform (f(c)) and that of the sinusoidal reference waveform (f(r)) have an integer ratio, that is, f(c) f(r)(-1) = k, k is an element of N. This strategy results into a model ('first-order differential equation based model') which can be readily developed for the SMCs with any number of levels expediting the investigation of their performance. Numeric computation results of the proposed analytic model for the SMCs and simulation results as well as measurements taken from an experimental set-up are presented in order to validate the suggested approach and derived model.

关键词： Bessel functions differential equations Fourier series numerical analysis PWM power convertors single-phase stacked multicell multilevel converters Kapteyn series Fourier–Bessel series analytical modelling mathematical model stacked multicell converters natural voltage balancing dynamics start-up behaviour dynamic response natural voltage balancing phenomenon closed-form analytic solution derivation switching functions phase disposition phase-shifted carrier pulse-width modulation Fourier coefficients pertinent PD–PSC-PWM modulator PD–PSC-PWM technique triangular carrier waveform sinusoidal reference waveform integer ratio first-order differential equation based model numeric computation

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An efficient technique to select logic nodes for single event transient pulse-width reduction

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MICROELECTRONICS RELIABILITY 2013年第1期53卷 114-117页

作者： Mahatme, Nihaar N. Chatterjee, Indranil Patki, Akash Limbrick, Daniel B. Bhuva, Bharat L. Schrimpf, Ronald D. Robinson, William Vanderbilt Univ Dept Elect Engn & Comp Sci Nashville TN 37212 USA

An efficient method has been developed to identify logic nodes most likely to generate single-event transients due to p-hits or n-hits. This is weighed against the logical masking effect of gates. Selected gates are hardened by increasing widths of only the restoring devices to reduce single-event error rate. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： SINGLE event effects (Electronics) ERROR rates TRANSIENTS (Electricity) LOGIC circuits pulse modulation (Electronics) pulse-width modulation

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A Hybrid Amplitude/Time Encoding Scheme for Enhancing Coding Efficiency and Dynamic Range in Digitally Modulated Power Amplifiers

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IEEE JOURNAL ON EMERGING AND SELECTED TOPICS IN CIRCUITS AND SYSTEMS 2013年第4期3卷 498-507页

作者： Xia, Jingjing Garg, Siddharth Boumaiza, Slim Univ Waterloo Dept Elect & Comp Engn Waterloo ON N2L 3G1 Canada

architecture for practical and highly efficient software-defined radio transmitters. Signal encoding schemes for DMPAs have primarily focused either on amplitude or time domain encoding, neither of which can simultaneously provide high coding efficiency, high dynamic range and low design complexity. In this paper, we propose, analyze and evaluate a new hybrid amplitude/ time signal encoding scheme that significantly improves the coding efficiency and dynamic range of DMPAs without significantly increasing design complexity. The proposed hybrid amplitude/time encoding scheme combines both the amplitude domain and the time domain to optimally encode information. Evaluation results show that hybrid amplitude/time encoding yields a 35% increase in the average coding efficiency with respect to conventional time encoding, and is only 6.7% lower than peak efficiency when applied to a Wireless Local Area Network signal with a peak to average power ratio equal to 9.9 dB. A new DMPA architecture, based on the proposed hybrid encoding, is also proposed.

关键词： Digital encoder digitally modulated power amplifier pulse-width modulation software-defined ratio

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Broadband difference frequency mixing between visible and near-infrared pulses for few-cycle pulse generation with stable carrier-envelope phase

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APPLIED PHYSICS B-LASERS AND OPTICS 2013年第1期113卷 19-25页

作者： Bradler, Maximilian Homann, Christian Riedle, Eberhard Univ Munich Lehrstuhl BioMol Opt D-80538 Munich Germany

Difference frequency generation between broadband visible noncollinear optical parametric amplifier (NOPA) pulses and the fundamental pump laser pulses allows the generation of ultrashort infrared pulses with passively stabilized carrier-envelope phase. A simple prism compressor for the visible NOPA pulses is sufficient to generate few-cycle pulses in the infrared and no additional compression is needed. We theoretically investigate the concept, explain the principles, and demonstrate it for high repetition rate, long pulse durations, and various wavelengths by applying it to a Ti:sapphire and an Yb:KYW-based laser systems. For the latter sub-15 fs phase stable pulses around 1.8 mu m with an energy of 100 nJ are obtained at 100 kHz repetition rate.

关键词： OPTICAL parametric amplifiers ULTRASHORT laser pulses LASERS -- Pumping PHASE transformations (Physics) WAVELENGTHS YTTERBIUM pulse-width modulation

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LABORATORY EVALUATION OF A TURN COMPENSATION CONTROL SYSTEM FOR A GROUND SPRAYER

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APPLIED ENGINEERING IN AGRICULTURE 2013年第5期29卷 655-662页

作者： Porter, W. M. Rascon, J. A. Shi, Y. Taylor, R. K. Weckler, P. A. Oklahoma State Univ Dept Biosyst & Agr Engn Stillwater OK 74078 USA

The ability to compensate sprayer nozzle flow across a horizontal boom has the potential to mitigate the problem of inaccurate chemical application rate due to lateral speed differences when sprayers are turning. A laboratory testing platform and procedure were developed and tested with a commercial turn compensation control system for a ground sprayer Virtual paths consisting of simulated GPS signals representing right and left turns separated by straight segments were simulated with four turning radii (75%, 125%, 250%, and 500%) based on boom width. Actual application rates from 11 nozzles spread across the boom were measured using load cells in real time and were compared with desired application rate. Mean flow rate and coefficient of variation by nozzle position for each segment of the test paths showed a general consistency between the expected application rate and actual application rate for most nozzles at most cases with a small discrepancy for a few nozzles. Application errors were within the accepted 10% range specified by ASABE. This study contributes to the formation of a test standard for turn compensation control systems calibration in the future.

关键词： pulse-width modulation Spray misapplication Contour spraying GPS Rate control

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Single-phase, 17-Level Hybridized Cascaded Multi-level Inverter

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ELECTRIC POWER COMPONENTS AND SYSTEMS 2013年第2期41卷 182-196页

作者： Odeh, Charles I. Nnadi, Damian B. N. Univ Nigeria Dept Elect Engn Nsukka 410001 Nigeria

This article proposes a single-phase, 17-level, cascaded multi-level inverter topology. The multi-carrier, phase disposition pulse-width modulation scheme is employed to generate the gating signals for the power switches. Operational principles with switching functions are given. By controlling the modulation index, the desired number of levels: 3 through 17, of the inverter's output voltage can be achieved. The validity of the proposed cascaded multi-level inverter is verified through simulation and experimental results.

关键词： inverter multi-level pulse-width modulation H-bridge

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pulse-width modulated external resistance increases the microbial fuel cell power output

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BIORESOURCE TECHNOLOGY 2013年 147卷 65-70页

作者： Coronado, J. Perrier, M. Tartakovsky, B. Ecole Polytech Montreal Dept Genie Chim Ctr Ville Montreal Montreal PQ H3C 3A7 Canada Natl Res Council Canada Montreal PQ H4P 2R2 Canada

This study describes MFC operation with a pulse-width modulated connection of the external resistor (R-PWM mode) at low and high frequencies. Analysis of the output voltage profiles acquired during R-PWM tests showed the presence of slow and fast dynamic components, which can be described by a simple equivalent circuit model suitable for process control applications. At operating frequencies above 100 Hz a noticeable improvement in MFC performance was observed with the power output increase of 22-43% as compared to MFC operation with a constant external resistance. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.

关键词： MFC Periodic operation pulse-width modulation Power output maximization

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Predictive variable-structure system control of unity power factor rectifiers

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IET POWER ELECTRONICS 2013年第8期6卷 1608-1617页

作者： Korelic, Joze Jezernik, Karel Univ Maribor FERI SLO-2000 Maribor Slovenia

This study presents the design of a current control loop and the selection of switching logic for pulse-width modulation (PWM) of three-phase switching converters. This approach is based on a deliberate introduction of the predictive sliding mode motion within a control system. It shows that the selection of the PWM pattern is a direct result of sliding mode existence within the current control closed-loop system. The design specifications are robustness to load electrical parameters, fast dynamic response, reduced switching frequency and simple hardware implementation. To meet previous specifications, a sliding mode controller has been developed, designed as a finite state machine, and implemented within a field programmable gate array device. The switching strategy implemented within the state transition diagram provides for a minimum number of switch state changes by the three-phase converter that is confirmed through simulation and experimental results.

关键词： control system synthesis dynamic response electric current control field programmable gate arrays finite state machines load regulation power factor predictive control PWM power convertors PWM rectifiers rectifying circuits robust control switching convertors variable structure systems three-phase switching converter state transition diagram field programmable gate array device finite state machine switching frequency reduction fast dynamic response robustness load electrical parameter current control closed-loop design system predictive sliding mode motion control system PWM pulse-width modulation switching logic selection unity power factor rectifier predictive variable-structure system control

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