849 research outputs found
Modulação vetorial aplicada a retificadores trifásicos PWM unidirecionais
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica.Este trabalho apresenta a aplicação da modulação vetorial a retificadores trifásicos PWM unidirecionais de dois níveis. Os conceitos da modulação vetorial e controle vetorial são introduzidos, tomando como exemplo a aplicação destas técnicas de controle e modulação ao retificador trifásico PWM bidirecional. Estratégias de modulação vetorial são propostas para os retificadores unidirecionais conectados em Y, ? e em ponte. Verifica-se a validade da extensão das técnicas de modulação propostas à outros retificadores e define-se uma metodologia generalizada para aplicação da modulação vetorial aos retificadores unidirecionais de dois níveis. São analisadas as estruturas de controle vetorial e a adaptação da modelagem proposta a cada tipo de retificador. Os projetos das estruturas de potência e de controle digital com DSP são realizados e os resultados da aplicação da modulação vetorial aos retificadores trifásicos são verificados através de simulação digital e da experimentação de um protótipo de 20kW. Os retificadores implementados apresentam alto rendimento, baixa taxa de distorção harmônica para as correntes de entrada e elevado fator de potência
New Stationary Frame Control Scheme for Three Phase PWM Rectifiers Under Unbalanced Voltage Dips Conditions
No full textA new stationary frame control scheme for three-phase pulsewidth-modulation (PWM) rectifiers operating under unbalanced voltage dips conditions is proposed in this paper. The proposed control scheme regulates the instantaneous active power at the converter poles to minimize the harmonics of the input currents and the output voltage ripple. This paper's novelty is the development of a new current-reference generator implemented directly in stationary reference frame. This allows using proportional sinusoidal signal integrator (P-SSI) controllers for simultaneous compensation of both positive and negative current sequence components. No phase-locked loop (PLL) strategies and coordinate transformations are needed for the proposed current-reference generator. Experimental results are presented for a 20-kV A alternative current (ac)/direct current (dc) converter prototype to demonstrate the effectiveness of the proposed control scheme. A comparison with two other existing control techniques is also performed. Fast dynamic performance with small dc-link voltage ripple and input sinusoidal currents are obtained with this control scheme, even under severe voltage dips operating condition
Repetitive current control of two-level and interleaved three-phase PWM utility connected converters
No full textThis thesis is mainly concerned with investigations into digital repetitive current controlof two-level and interleaved utility connected PWM converters. The research ismotivated by the relatively poor performance of classical (PI) controllers when theutility voltage harmonic distortion is high. This is due to the low gain, and poordisturbance rejection of the PI controller at the utility harmonic frequencies. Repetitivefeedback controllers have the ability to track or reject periodic disturbances, such asutility harmonics, as they naturally have high gains at the utility voltage harmonicfrequencies, assuming that these frequencies do not change.Repetitive controllers (RC) are known for being sensitive to variations in systemparameters and disturbance frequency, which in practice renders them either ineffectiveor unstable. Another challenge arises from the memory requirements of RC in case ofthe absence of even harmonics, which can make its practical implementation difficultand expensive. In addition, another problem that has not been investigated extensivelyin the literature is that the effectiveness of RC is severely limited by the limitedbandwidth of the plant (the utility connected converter and its filter). Theoreticalanalysis and simulation results presented in this thesis show that RC could noteffectively reject disturbances at frequencies above the closed loop system bandwidth.The design of the converter's output filter bandwidth and the values of its componentsneed to be selected carefully, to enable RC to be used effectively.The research in this thesis focuses on investigating the practical implementation andperformance limits of two types of repetitive controllers (conventional and oddharmonics),used for current control of two-level utility connected converter with LCLoutput filter. The odd-harmonic repetitive controller halves the memory requirementand offers higher gains only at odd harmonic frequencies of interest. The overall controlscheme consists of the traditional classical tracking controller with a dual loop feedbacksystem and RC. The results indicate that the repetitive controller improves the steadystate error and the total harmonic distortion of the output current, provided that theplant's bandwidth is sufficiently large.Finally, a repetitive controller for an interleaved utility connected converter has beendesigned and investigated in this study. The interleaved converter system has higherbandwidth than the two-level converter, which improves the effectiveness of RC. Itprovides good disturbance rejection compared to classical controllers which results inlow output current THD. The RC was demonstrated to be robust despite uncertainty inutility impedance, while achieving a fast almost zero error convergence. The proposedRC has been experimentally implemented using a DSP and the results indicate that thequality of output current complies with international standards on harmonic limits andmatches simulation results obtained from the Matlab/Simulink model of the system
Transient voltage distribution along LV motor windings fed with PWM converters. Insulation ageing analysis
No full textIron Losses Prediction with PWM Supply Using Low and High Frequency Measurements: Analysis and Results Comparison
No full textIn this paper, two different methods for iron loss prediction are analyzed. The first method is based on the classical separation of loss contributions (hysteresis, eddy-current, and excess losses). The model requires loss contribution separation using iron loss measurements with sinusoidal supply. In this paper, this method will be called the ldquolow-frequency method.rdquo The second method, named the ldquohigh-frequency method,rdquo is based on the assumption that, under pulsewidth modulation supply, the higher order flux density harmonics do not influence the magnetic work conditions. These magnetic conditions depend only on the amplitude of the fundamental harmonic of the flux density. In this paper, both the proposed methodologies and the related measurements are described in detail, and the obtained results are compared with the experimental ones. The experimental results show that both methods allow getting excellent results. The high-frequency method is better than the lower one but requires a more complex test bench. Depending on the accuracy required by the user, the more handy method can be chosen, with the guarantee that the estimation errors will be lower than 5
Multiple sets of solutions for harmonic elimination PWM bipolar waveforms: Analysis and experimental verification
No full textMultiple sets of solutions for the selective harmonic elimination pulse-width modulation method for inverter control exist. These sets present an independent solution to the same problem but further investigation reveals that certain sets may offer an improved overall harmonic performance. In this paper, a minimization method is discussed as a way to obtain these multiple sets of switching angles. A simple distortion harmonic factor that takes into account the first two most significant harmonics present in the generated waveform is considered in order to evaluate the performance of each set. The bipolar waveform is thoroughly analyzed and two cases are considered; single-phase patterns which eliminate all odd harmonics and three-phase counterparts which eliminate only the nontriplen odd harmonics from the line-to-neutral pattern but such harmonics are naturally eliminated from the line-to-line waveform. Experimental results support the theoretical considerations reported in the paper
Microprocessor-Based Interactive PWM Inverter
No full textMicroprocessor-based interactive PWM inverter A novel method of implementing an on-line interactive PWM inverter controller is presented. It uses a real-time operating system with an active and standby memory band concept. Only the active band is used in the actual control and the standby band is for editing. After updating, the two bands are flipped. </jats:sec
A chaotic PWM motor drive for electric propulsion
No full textIn this paper, a chaotic Pulse width modulation (PWM) closed-loop induction motor drive is proposed and implemented to improve the electromagnetic compatibility (EMC) for electric propulsion. The key is to propose a chaotically amplitude-modulated frequency modulator (CAFM) to modulate the space vector PWM (SVPWM), in such a way that the CAFM-SVPWM scheme is proposed for the vector controlled induction motor drive. By designing the CAFM properly, the proposed CAFM-SVPWM scheme can not only decrease the peaky electromagnetic interference (EMI) but also avoid the mechanical resonance in induction motor drives. Thus, it affords better spectrum performance than the fixed frequency PWM and random frequency PWM induction motor drives. Also, the proposed chaotic PWM induction motor drives could provide good steady-state as well as transient operating performance for electric propulsion. Both simulation and experimental results are given to verify the validity of the proposed chaotic PWM motor drives. © 2008 IEEE.link_to_subscribed_fulltex
Development of a grid emulator for network integration studies
No full textIncludes bibliographical references.The economic and environmental side effects of fossil fuels have forced governments and authorities to investigate sustainable solutions. Main interest is focused on environment friendly benefits, provided by renewable energy sources. The growth rate of these energy sources has increased remarkably in the past few years. Correspondingly the research and development in the field of power electronics has also increased, especially in medium voltage and high power grid connected systems. The grid behaviour of the renewable energy systems is heavily influenced by the control techniques of these systems. For further development of these control methods the most basic and conventional way is to simulate, test and prove the system performance on a down-scaled lab test bench. The objective of this thesis is to develop a laboratory test bench grid emulator for network integration studies. Design and performance are investigated by introducing several kinds of unbalanced voltage conditions to test the behavior of connected systems. Voltage dips and swells are implemented to test the system’s performance
PWM-based Transthoracic Bioimpedance Analyzer for Detecting Heart Failures
No full textPatients that suffer from heart failure can benefit from wearable monitoring devices that continuouslymonitor the condition of the heart. One of the foremost symptoms of exacerbation of the heart is fluidcongestion in the lungs. One of the method to measure a change in biological tissue, such as thebuildup of fluids in the lungs and chest, is bioimpedance measurements. By injecting an alternatingcurrent into the tissue, a voltage develops across the tissue that is proportional to the impedance ofthe biological tissue, the bioimpedance. Conventional bioimpedance measurement techniques are notsuitable for continuous monitoring of the patients as they are power consuming and hinder patient intheir daily living.This thesis proposes an alternative approach that is based on a pulse width modulation (PWM) inorder to convert the measured analog signals to time signals. To determine the measured bioimpedance, the magnitude and phase should be derived. The proposed design employs one channel toconvert the measured voltage across the bioimpedance to a PWM signal. As this PWM signal contains the amplitude information of the measured voltage, the magnitude of the bioimpedance can bederived. Furthermore, a second reference channel is employed where a known resistive reference isconverted to another PWM signal. By comparing the two PWM signals, the phase of the bioimpedancecan be determined. The proposed system requires only a comparator and triangular wave in order toconvert the measured analog signals, compared to the complex implementation of the conventionallyused analogtodigital converter.In order to validate the design, the circuit is simulated and implemented on a printed circuit board (PCB). The PCB operates correctly on 3.3V and, additionally, an voltagecontrolled current sourceis implemented and connected externally to the PCB to provide an excitation current of 100μA and10kHz to the circuit. The circuit should be capable of measuring the voltage across a device under test(퐷푈푇) that consist of resistive and capacitive components. This is because the bioimpedance can bemodelled by the FrickeMorse model, which consist of a resistor in parallel with a capacitor and resistorin series. The implemented PCB can measure 퐷푈푇 magnitudes up to 1kΩ and is determine the phaseshift between the two PWM signals.This work shows an important contribution towards a wearable continuous bioimpedance measurements system to monitor patient that suffer from heart failure. It has been shown that the presenteddesign can measure the magnitude and phase that are required to determine the measured bioimpedance, and also reduce complexity of the measurements instrumentation
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