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1
Yatim, Abdul Halim bin Mohamed. "A microprocessor controlled three-phase insulated gate transistor PWM inverter drive." Thesis, University of Bradford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292639.
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Ad'doweesh, K. E. "A microprocessor based PWM inverter drive incorporating a three-phase induction motor." Thesis, University of Bradford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371459.
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Engku, Ariff E. A. R. B. "Space vector Pwm techniques for six-phase three-level inverter-fed drives." Thesis, Liverpool John Moores University, 2018. http://researchonline.ljmu.ac.uk/7982/.
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In recent years, research in the area of multiphase drives has increased significantly. Having higher number of machine phases allows the current to be shared between the phases, thus reducing the current rating of power semiconductors used in the power converter. Additionally, if a multilevel inverter is used to drive the machine, the output voltage waveforms are going to be approximated closer toward sinusoidal waveforms, thus resulting in lower total harmonic distortion. Therefore, the combination of multiphase and multilevel technologies gives considerable benefits compared to conventional two-level three-phase drives. Unlike a carrier-based approach, which can be easily expanded to any number of converter voltage levels and any number of machine phases, the development of space vector algorithms is also reliant on the machine’s configuration. In other words, different drive topologies require their own unique space vector algorithms. In fact, the complexity of developing a space vector algorithm will dramatically increase with the increase of number of levels and/or number of phases. This thesis presents pulse width modulation techniques for two- and three-level asymmetrical and symmetrical six-phase drives with a single or two isolated neutral points configuration. However, since the modulation techniques for the drives with two isolated neutral points are based on the well-established modulation techniques for three-phase drives, more emphasis is given towards the development of modulation techniques for single neutral point case, particularly those that are based on space vector algorithm principles. In order to realise sinusoidal output phase voltage waveforms, several requirements and conditions have to be met. The requirements revolve around ensuring that the low order harmonics, which contribute to the machine losses, will not exist. Meanwhile, the conditions are more towards minimising the switching losses. All modulation techniques are verified through simulation, while those for three-level case are validated experimentally as well. Comparison and discussion of obtained simulation and experimental results, performance and complexity in terms of execution time of the developed modulation techniques, are presented. The equivalence between corresponding modulation techniques, which are based on the space vector algorithm and carrier-based approach are also established.
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Hussien, Zahrul Faizi. "Current control of three-phase PWM Inverter for flywheel energy storage system." Thesis, University of Southampton, 2000. https://eprints.soton.ac.uk/47946/.
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The thesis is concerned with the use of flywheel energy storage system (FESS) in utility load levelling application. The work presented consists of two parts, first, an evaluation of utility load levelling schemes with FESS as the energy storage medium, and second, the development of power electronic interface of FESS to the utility. The thesis presents a study to evaluate FESS load levelling schemes in a UK electricity supply and distribution company. It identifies and quantifies the costs and benefits of the schemes, and carries out a financial appraisal based on Net Present Value (NPV) and Internal Rate of Return (IRR) methods. The results indicate that the DSM schemes utilising FESS can be financially viable for a UK electricity supply and distribution business in a mass-produced (low-cost) FESS scenario, and provide FESS manufacturers and developers with cost goals for such applications. The conclusions drawn provide the motivation for further technical research undertaken within the programme of work. The main work presented is in the area of power electronic interface between FESS, as well as other energy storage devices or energy sources, and the utility for embedded generation. The thesis particularly focuses on the design of current controllers for an interface in the form of three-phase voltage-source pulsewidth modulated (VS-PWM) inverter connected to the utility via LCL filter. Two different current controller structures based on suboscillation current control method have been analysed and designed, aided by computer simulation studies carried out using a general purpose dynamic system simulation software, Matlab Simulink. General properties of a three-phase VS-PWM inverter have been investigated to establish a basic understanding of its operation. The phenomenon of phase interaction in a system with no neutral connection has been examined and the effect of practical inverter nonlinearities caused by interlock time delay (dead time) and on-state voltage drops of the semiconductor devices has been discussed. Various PWM current control techniques have been investigated, including the three-independent hysteresis current control, advanced hysteresis current control, suboscillation current control and space vector current control. The suboscillation current control method has been chosen as produces a well defined harmonic spectrum in the output current without the need for complicated computations and extensive hardware, and can be easily implemented in analogue to avoid problems •sampling and computation time delay generally associated with digital controllers. Fundamental appreciation of the suboscillation PWM technique has been established from analytical synthesis of the modulation process, providing a rational basis for the current controller and computer simulation model validation. An inherent disadvantage of the suboscillation control method has been found to be its limited controller gain, causing a steady-state error to and the effect of inverter nonlinearities to be quite significant. In the first current controller structure, a simple compensation has been utilised to enable the gain to be increased beyond the conventional limit. Simulation results show that the steady-state error the current waveform has been improved and the effect of inverter nonlinearities has been It also makes the current controller less susceptible to the inherently noisy environment, current controller has been experimentally built and tested to validate the simulation results and to validate the practical aspects of its implementation. In the second current controller structure, a cyclic feedback system based on Iterative Control (ILC) has been utilised to eliminate the periodic error in the current waveform. The structure is more complicated and the cyclic feedback system requires digital implementation. Simulation results indicate that the cyclic feedback system is effective in eliminating periodic error in the current waveform. Due to time constraints and hardware limitations, ital implementation of the system has not been possible but is recommended for future research.
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Un, Emre. "Common Mode Voltage And Current Reduction In Voltage Source Inverter Driven Three Phase Ac Motors." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609062/index.pdf.
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In this thesis various reduced common mode voltage (RCMV) pulse width modulation (PWM) techniques and active/passive common mode voltage (CMV) reduction methods for voltage source inverter driven three-phase AC motors are theoretically and practically investigated. A novel RCMV-PWM method, the near state PWM (NSPWM) method is proposed for operation at high modulation index. At low modulation index, a modified version of an existing RCMV-PWM method, AZSPWM1, termed as MAZSPWM, is proposed to mitigate the voltage reflection problem of the method. An optimum modulation algorithm combining NSPWM and MAZSPWM with seamless transition is proposed. The proposed RCMV-PWM methods significantly reduce CMV but they suppress common mode current (CMC) partially. Utilization of a common mode inductor together with RCMV-PWM methods is effective in suppressing the CMC. In the study, in addition to the CMV characteristics, various practical performance characteristics such as voltage linearity, inverter output current ripple, inverter DC-link current ripple, and output line-to-line voltage pulse pattern are also analyzed. The study involves analysis, computer simulations, and detailed laboratory experiments.
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Pou, Félix Josep. "Modulation and control of three-phase PWM multilevel converters." Doctoral thesis, Universitat Politècnica de Catalunya, 2002. http://hdl.handle.net/10803/6327.
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La present tesi doctoral estudia els inversors trifàsics multinivell del tipus denominat de díodes de fixació (diode-clamped converters). Aquests convertidors poden generar tres o més nivells de tensió a cada fase de sortida, i normalment s'apliquen a sistemes de gran potència ja que poden treballar amb tensions majors que els inversors clàssics. L'anàlisi es centra fonamentalment en la topologia de tres nivells, tot i que també es realitzen contribucions per a convertidors de més nivells. Els principals objectius són la proposta de nous algorismes de modulació vectorial PWM de processat ràpid, l'estudi i la compensació dels efectes dels desequilibris de les tensions dels condensadors del bus de continua, i l'anàlisi de llaços de control avançat.S'han desenvolupat diversos models que han permès obtenir resultats de simulació de les tècniques de modulació i control proposades. A més, gràcies a l'estada d'un any de l'autor al Center for Power Electronics Systems (CPES) a Virginia Tech, USA, la tesi també inclou resultats experimentals que consoliden les conclusions i metodologies presentades. Les principals contribucions es resumeixen a continuació.
Es presenta un nou algorisme de modulació vectorial PWM que aprofita simetries del diagrama vectorial per a reduir el temps de processat. S'analitzen i es quantifiquen les oscil·lacions de tensió de baixa freqüència que apareixen en el punt central dels condensadors del convertidor de tres nivells. Aquesta informació permet dimensionar els condensadors donades les especificacions d'una determinada aplicació.
L'algorisme de modulació també s'aplica a convertidors de més nivells. Pel cas concret del convertidor de quatre nivells, es comprova l'existència de corrents continus en els punts mitjos dels condensadors que fan que els sistema sigui inestable. Es determinen gràficament les zones d'inestabilitat.
Es presenta un nou i eficient algorisme de modulació vectorial feedforward en el convertidor de tres nivells que és capaç de generar tensions trifàsiques de sortida equilibrades, malgrat l'existència de desequilibris en les tensions dels condensadors.
S'estudien els efectes negatius de càrregues lineals desequilibrades i càrregues no lineals en el control de les tensions dels condensadors. Es justifica que l'existència d'un quart harmònic en els corrents de càrrega pot inestabilitzar el sistema. És determina la màxima amplitud tolerable d'aquest harmònic.
S'estudia la millora en l'equilibrat de les tensions d'una connexió de dos convertidors de tres nivells al mateix bus de continua (back-to-back connection). Un exemple d'aplicació pràctica és la conversió AC/DC/AC per a l'accionament de motors d'alterna treballant amb factor de potència unitari.
Finalment s'aplica un controlador òptim al convertidor de tres nivells treballant com a rectificador elevador (boost). El llaç de control LQR (Linear Quadratic Regulator) es simplifica donat que la tasca d'equilibrat de les tensions dels condensadors es dur a terme en el mateix modulador.
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Afiat, Milani Alireza. "Voltage regulation in a single-stage three-phase boost-inverter using modified phasor pulse width modulation method for stand-alone applications." Thesis, Kansas State University, 2013. http://hdl.handle.net/2097/16219.
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Master of ScienceDepartment of Electrical and Computer Engineering
Behrooz Mirafzal
In this thesis, a modified version of the phasor pulse width modulation (PPWM) switching method for use in a single-stage three-phase boost inverter is presented. Because of the required narrow pulses in the PPWM method and limitations in controller resolution, e.g. dSPACE, the desired switching pattern for a boost inverter requires a costly processor. A low resolution processor can cause pulse dropping which results in some asymmetric conditions in output waveforms of the boost inverter and therefore, an increase in the THD of the output waveform. In order to solve this problem, a new switching pattern is developed which guarantees symmetric conditions in the switching pattern by discretizing the switching pattern in every switching cycle. This switching pattern has been applied to a boost inverter model developed by SimPowerSystems toolbox of MATLAB/Simulink. The model has been simulated in a wide range of input DC voltage and load. Moreover, a laboratory-scaled three-phase boost inverter has been designed, built, and tested using an identical switching pattern in the same input voltage and load range. Both simulation and experimental results confirm the effectiveness of the new switching pattern.
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Ayhan, Ufuk. "Investigation Of Dc Bus Current Harmonics In Two And Three Level Three-phase Inverters." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614182/index.pdf.
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Within scope of this work, double-fourier analysis method of rapid calculation and
detailed simulation method, which are used to investigate DC bus current harmonics
in two level and three level three-phase inverters systematically, will be emphasized
and two methods will be compared via applying different modulation techniques. In
addition, DC bus currents will be investigated visually for various working
conditions and modulation methods. After that, analysis methods will be applied
and harmonic spectrums will be determined. After all, it will be showed that
calculated harmonic spectrums could be treated as unified harmonics around certain
frequencies and these unified harmonics could be reached easily via looking at
predetermined table. Moreover, it will also be showed that unified harmonic values
could be used to determine harmonic current components that are necessary for
sizing DC bus capacitor and could be used in various inverter analysis.
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Cetin, Nebi Onur. "Design And Implementation Of Advanced Pulse Width Modulation Techniques And Passive Filters For Voltage Source Inverter Driven Three-phase Ac Motors." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612236/index.pdf.
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Advanced pulse width modulation (PWM) techniques such as space vector PWM, active zero state PWM, discontinuous PWM, and near state PWM methods are used in three-phase AC motor drives for the purpose of obtaining low PWM current ripple, wide voltage linearity range, and reduced common mode voltage (CMV). In some applications, a filter is inserted between the inverter and the motor for the purpose of reducing the stresses in the motor. The motor current PWM ripple components, terminal voltage overshoots, shaft voltage, and bearing currents, etc. can all be reduced by means of PWM techniques and passive filters. Various PWM techniques and passive filter types exist. This thesis studies the combinations of PWM techniques and filters and evaluates the performance of the motor drive in terms of the discussed stresses in the motor. PWM techniques are reviewed, a generalized algorithm for the implementation of PWM techniques is developed, and implementation on a 4 kW rated drive is demonstrated. Filter types are studied, among them the common mode inductor and the pure sine filter (PSF) configurations are investigated in detail. Filters are designed and their laboratory performance is evaluated. In the final stage the advanced PWM techniques and filters are combined, the incompatibility problem of discontinuous PWM methods with the PSF is illustrated. A cure based on rate of change limiter is proposed and its feasibility proven in the laboratory experiments. With the use of the proposed PWM algorithm and PSF, a motor drive with ideal DC to AC conversion stage (DC to pure sine) is achieved and its performance is demonstrated in the laboratory.
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Demirkutlu, Eyyup. "Output Voltage Control Of A Four-leg Inverter Based Three-phase Ups By Means Of Stationary Frame Resonant Filter Banks." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608151/index.pdf.
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A method for high performance output voltage control of a four-leg inverter based three-phase transformerless UPS is proposed. Voltage control loop is employed and the method employs stationary frame resonant filter controllers for the fundamental and harmonic frequency components. A capacitor current feedback loop provides active damping and enhances the output voltage dynamic performance. The
controller design and implementation details are given. Linear and nonlinear loads for balanced and unbalanced load operating conditions are considered. The steadystate
and dynamic performance of the UPS are investigated in detail. A scalar PWM method with implementation simplicity and high performance is proposed and implemented. The control and PWM methods are proven by means of theory,
simulations, and experiments.
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Cetinkaya, Suleyman. "Repetitive Control Of A Three-phase Uninterruptible Power Supply With Isolation Transformer." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608150/index.pdf.
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A repetitive control method for output voltage control of a three phase uninterruptible power supply (UPS) with isolation transformer is investigated. In the method voltage control loop is employed in the stationary dq frame. The controller eliminates the periodic errors on the output voltages due to inverter voltage nonlinearity and load disturbances. The controller design and implementation details are given. The controller is implemented on a 5-kVA UPS prototype which is
constructed in laboratory. Linear and nonlinear loads for balanced and unbalanced load operating conditions are considered. The steady-state and dynamic performance of the control method are investigated in detail. The theory of the control strategy is verified by means of simulations and experiments.
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Silva, Carlos Elmano de Alencar e. "Estudo e desenvolvimento experimental de um sistema eÃlico interligado a rede elÃtrica." Universidade Federal do CearÃ, 2012. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=7458.
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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorFundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico
Este trabalho apresenta o estudo e desenvolvimento de um sistema eletrÃnico de aproveitamento de energia eÃlica a partir de um gerador sÃncrono de Ãmà permanente conectado a uma turbina de vento. O sistema opera com velocidade variÃvel, permitindo o mÃximo aproveitamento da energia cinÃtica incidente na turbina de vento. Essa energia cinÃtica à convertida em energia elÃtrica pelo gerador sÃncrono de Ãmà permanente e depois de totalmente condicionada, injetada na rede elÃtrica convencional. Esse condicionamento à feito por um sistema eletrÃnico objeto de estudo e desenvolvimento deste trabalho, o qual consiste em um retificador trifÃsico interligado a um inversor monofÃsico em ponte completa com saÃda em corrente. SÃo apresentadas a revisÃo bibliogrÃfica de sistemas de aproveitamento de energia eÃlica para geraÃÃo de energia elÃtrica pertinentes ao escopo do trabalho, a anÃlise do estÃgio retificador (potÃncia e controle), a anÃlise do estÃgio inversor (potÃncia e controle), uma comparaÃÃo teÃrica de rendimento entre o retificador trifÃsico proposto neste trabalho (bridgeless trifÃsico) e o retificador trifÃsico dois nÃveis, e os resultados experimentais de um protÃtipo de validaÃÃo de 5kW do sistema proposto.
This work presents the study and development of an electronic system for wind energy exploitation from a permanent magnet synchronous generator connected to a wind turbine. The system operates with variable speed, allowing maximum use of the kinetic energy incident on the wind turbine. This kinetic energy is converted into electrical energy by the permanent magnet synchronous generator and, after being fully conditioned, injected into the conventional power grid. This conditioning is done by an electronic system object of study and development of this work, which consists of a rectifier connected to a single-phase full-bridge inverter with current output. Are presented the literature review of the relevant wind energy conversion systems to the scope of work, the analysis of the rectifier stage (power and control), the analysis of the inverter stage (power and control), a efficiency theoretical comparison between the proposed rectifier (three-phase bridgeless) and the three-phase fullbridge rectifier, and the experimental results of an 5kW validation prototype of the proposed system.
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Rutkovskiy, Yaroslav. "A Novel Control Method for Grid Side Inverters Under Generalized Unbalanced Operating Conditions." Cleveland State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=csu1610646102417883.
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Clark, Paul R. "Optimum PWM strategies for microprocessor controlled three phase inverters." Thesis, University of Bristol, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357755.
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Barden, Alisson Thomas. "Projeto e análise de controladores robustos aplicados a inversores trifásicos de fontes ininterruptas de energia (UPS)." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/141945.
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O objetivo principal deste trabalho é o desenvolvimento de controladores robustos baseados no princípio do modelo interno, em referenciais síncrono e estacionário, para aplicação ao estágio de saída de uma fonte ininterrupta de energia (UPS) a fim de minimizar a distorção na tensão de saída causada pela conexão de cargas não lineares balanceadas e desbalanceadas. A formulação em referencial estacionário (abc) é realizada através da aplicação de controladores com múltiplos modos ressonantes, a fim de se estabelecer erro nulo ao seguimento de referência senoidal e rejeição de distúrbios na tensão de saída devido às correntes com elevado conteúdo harmônico drenadas pelas cargas. Além disso, o controle é formulado em referencial síncrono (dq0) utilizando controladores Proporcional-Integral (PI) convencionais muito difundidos na maioria das aplicações comerciais de UPS. O projeto de ambos controladores é realizado utilizando uma metodologia de controle robusto com realimentação de estados, onde os parâmetros dos controladores são determinados através da resolução de um problema de otimização convexa sujeito a um conjunto de restrições na forma de desigualdades matriciais lineares (LMI). Uma análise comparativa de desempenho é realizada entre controladores com um modo ressonante (sintonizado na fundamental) e o PI em dq0, pois apresentam estruturas funcionalmente equivalentes sob a ótica do princípio do modelo interno aplicada a seus respectivos referenciais. Além do mais, demonstra-se a melhoria no desempenho com o uso dos controladores múltiplo ressonantes em referencial estacionário onde escolhe-se as frequências de ressonância de cada modo de maneira a suprimir os efeitos de harmônicas específicas na tensão de saída da UPS. A análise comparativa entre os controladores propostos é realizada através de simulações numéricas, utilizando os procedimentos de ensaio dinâmico e estático e as exigências estabelecidas pela norma internacional IEC 62040-3.The main objective of this work is the development of robust controllers based on the internalmodel principle, in synchronous and stationary frames, applied to the output stage of an uninterruptible power supply (UPS), in order to minimize the output voltage distortion caused by the connection of balanced and unbalanced nonlinear loads. The formulation in stationary abc-frame is accomplished through the aplication of a multiple resonant controller, so that, it is possible to achieve zero-error tracking of the sinusoidal reference and disturbances rejection on the output voltage due to the high amount of harmonic currents drained by the loads. Moreover, a controller in synchronous reference frame (dq0 axis) is formulated through the application of conventional Proportional-Integral (PI) controllers which are widely used in comercial UPS applications. The design of both controllers is formulated using a state-feedback robust controlmethod, in which the controller parameters are determined by solving a convex optimization problem subject to a set of LMI constraints. A comparative analysis on the performance of the single-mode resonant controller (tuned at the fundamental frequency) and the PI controller is performed, because these controllers are functionally equivalent in the sense of the internal model principle applied to their respective frames. Furthermore, the improvement in performance is demostrated with the use of multiple resonant controllers in stationary abc-frame where the resonance frequencies are chosen to suppress the effects of a specific harmonic in the UPS output voltage. The comparative analysis of the proposed controllers is performed through numerical simulations, making use of the dynamical and steady-state test methods and performance requirements defined by the IEC 62040-3 international stardard.
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Yildirim, Dogan. "Field Oriented Control Of A Permanent Magnet Synchronous Motor Using Space Vector Modulated Direct Ac-ac Matrix Converter." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614302/index.pdf.
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The study designs and constructs a three-phase to three-phase direct AC&ndashAC matrix converter based surface mounted permanent magnet synchronous motor (PMSM) drive system. First, the matrix converter topologies are analyzed and the state-space equations describing the system have been derived in terms of the input and output variables. After that, matrix converter commutation and modulation methods are investigated. A four-step commutation technique based on output current direction provides safe commutation between the matrix converter switches. Then, the matrix converter is simulated for both the open-loop and the closed-loop control. For the closed-loop control, a current regulator (PI controller) controls the output currents and their phase angles. Advanced pulse width modulation and control techniques, such as space vector pulse width modulation and field oriented control, have been used for the closed-loop control of the system. Next, a model of diode-rectified two-level voltage source inverter is developed for simulations. A comparative study of indirect space vector modulated direct matrix converter and space vector modulated diode-rectified two-level voltage source inverter is given in terms of input/output waveforms to verify that the matrix converter fulfills the two-level voltage source inverter operation. Following the verification of matrix converter operation comparing with the diode-rectified two-level voltage source inverter, the simulation model of permanent magnet motor drive system is implemented. Also, a direct matrix converter prototype is constructed for experimental verifications of the results. As a first step in experimental works, filter types are investigated and a three-phase input filter is constructed to reduce the harmonic pollution. Then, direct matrix converter power circuitry and gate-driver circuitry are designed and constructed. To control the matrix switches, the control algorithm is implemented using a DSP and a FPGA. This digital control system measures the output currents and the input voltages with the aid of sensors and controls the matrix converter switches to produce the required PWM pattern to synthesize the reference input current and output voltage vectors, as well. Finally, the simulation results are tested and supported by laboratory experiments involving both an R-L load and a permanent magnet synchronous motor load. During the tests, the line-to-line supply voltage is set to 26 V peak value and a 400 V/3.5 kW surface mounted permanent magnet motor is used.
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Abu-Sara, Mohammad. "Digital control of utility and parallel connected three-phase PWM inverters." Thesis, University of Southampton, 2004. https://eprints.soton.ac.uk/47947/.
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This thesis is mainly concerned with fundamental investigations into digital current control of utility-connected PWM inverters with output LCL filter whose capacitors are connected to the dc link rails. The thesis also presents analysis and evaluations of alternative three-level PWM inverters and alternative filter configurations. Additionally, the thesis presents investigations into parallel-connected PWM inverters. Various pulse width modulated (PWM) controllers including hysteresis and linear controllers have been reviewed. Hysteresis controller combines the current control task with the voltage modulation task. This makes the hysteresis controller unable to dampen resonance when used with an LCL filter and also unable to reject utility disturbance. On the other hand, linear controllers separate the current control task from the voltage modulation task. This allows exploitation of the advantages of open loop modulators including carrier based PWM (CB-PWM) and space vector modulation (SVM) such as constant switching frequency and well-defined harmonic spectrum. A linear digital current controller with CB-PWM has been analysed and designed, aided by computer simulation using Matlab Simulink. The controller structure is based on two feedback loops of the output current and the filter capacitor current, which has been shown to provide extra degree of freedom, and enables better controller performance compared to controllers with a one-feedback-loop structure. Additionally, the controller incorporates a feedforward loop to compensate for utility voltage disturbance. The effect of the processor computational time delay on system stability has been investigated using the modified Z-transform. The investigations have shown that the optimum sampling rate should be twice the PWM carrier frequency, and the optimum sampling instant should be synchronized with the peaks of the PWM carrier in order to minimize the effect of the current switching frequency ripple disturbance. However, in practice due to computational time delay, it is not possible sample at the peaks of the PWM carrier, which may result in distortion in the output current due to sampling of the switching frequency ripple. Hence a novel nonlinear time delay compensator that accurately calculates the variation in the capacitor current during time has been proposed and demonstrated to be effective in rejecting the switching ripple disturbance. In addition, a novel digital sampling scheme in which the sampling is delayed by half a PWM carrier cycle been proposed. Using this scheme combined with a time delay state observer, better switching disturbance rejection was achieved. The proposed current controller has been experimentally implemented using a digital signal processor DSP and the results have shown that the quality of the output current complies with the standards on harmonic limits for electricity distribution systems. An alternative three-level inverter structure has also been studied in order to reduce switching frequency ripple and hence the inductor cost. Simulation results have shown that filter inductor ripple current of a three-level inverter is on average half that of a two-level inverter but at the cost of extra power switches. A comparative study between different filter structures has also been carried out. It has been shown that connecting the capacitors to the dc-link decouples the phase and removes neutral voltage fluctuations with respect to the dc link. On the other hand, connecting the filter capacitor in delta or star, halves the inductor ripple current. Wireless control of parallel-connected PWM inverters using frequency and voltage drooping has been investigated to assess hardware and software requirements to implement such a system. The results have shown that this controller forces the inverters to share active power equitably, but good reactive power sharing requires a higher output inductor than that used in the current system.
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Nusair, Ibrahim Rakad. "Comparison Between PWM and SVPWM Three-Phase Inverters in Industrial Applications." Youngstown State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1355949821.
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Li, Yong. "Unified zero-current-transition techniques for high-power three-phase PWM inverters." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/26843.
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This dissertation is devoted to a unified and comprehensive study of zero-current-transition (ZCT) soft-switching techniques for high-power three-phase PWM inverter applications. Major efforts in this study are as follows: 1) Conception of one new ZCT scheme and one new ZCT topology; 2) Systematic comparison of a family of ZCT inverters; 3) Design, implementation and experimental evaluation of two 55-kW prototype inverters for electric vehicle (EV) motor drives that are developed based on the proposed ZCT concepts; and 4) Investigation of the ZCT concepts in megawatts high-frequency power conversions. The proposed ZCT techniques are also applicable to three-phase power-factor-correction (PFC) rectifiers.
In order to minimize switching losses, this work first proposes a new control scheme for an existing three-phase ZCT inverter circuit that uses six auxiliary switches. The proposed scheme, called the six-switch ZV/ZCT, enables all main switches, diodes and auxiliary switches to be turned off under zero-current conditions, and in the meantime provides an opportunity to achieve zero-voltage turn-on for the main switches. Meanwhile, it requires no modification to normal PWM algorithms. Compared with existing ZCT schemes, the diode reverse-recovery current is reduced significantly, the switching turn-on loss is reduced by 50%, the resonant capacitor voltage stress is reduced by 30%, and the current and thermal stresses in the auxiliary switches are evenly distributed.
However, a big drawback of the six-switch ZV/ZCT topology, as well as of other types of soft-switching topologies using six auxiliary switches, is the high cost and large space associated with the auxiliary switches. To overcome this drawback, this work further proposes a new three-phase ZCT inverter topology that uses only three auxiliary switches-- the three-switch ZCT. The significance of the proposed three-switch ZCT topology is that, among three-phase soft-switching inverters developed so far, this is the only one that uses fewer than six auxiliary switches and still has the following three features: 1) soft commutation for all main switches, diodes and auxiliary switches in all operation modes; 2) no modification to normal PWM algorithms; and 3) in practical implementations, no need for extra resonant current sensing, saturable cores, or snubbers to protect the auxiliary switches.
The proposed six-switch ZV/ZCT and three-switch ZCT inverters, together with existing ZCT inverters, constitute a family of three-phase ZCT inverters. To explore the fundamental properties of these inverters, a systematic comparative study is conducted. A simplified equivalent circuit is developed to unify common traits of ZCT commutations. With the visual aid of state planes, the evolution of the family of ZCT inverters is examined, and their differences and connections are identified. Behaviors of individual inverters, including switching conditions, circulating energy, and device/component stresses, are compared.
Based on the proposed six-switch ZV/ZCT and three-switch ZCT techniques, two 55-kW prototype inverters for EV traction motor drives have been built and tested to the full-power level with a closed-loop controlled induction motor dynamometer. The desired ZCT soft-switching features are realized together with motor drive functions. A research effort is carried out to develop a systematic and practical design methodology for the ZCT inverters, and an experimental evaluation of the ZCT techniques in the EV motor drive application is conducted. The design approach integrates system optimization with characterizations of the main IGBT device under the ZCT conditions, selection, testing and characterization of the auxiliary devices, design and selection of the resonant inductors and capacitors, inverter loss modeling and numerical analysis, system-level operation aspects, and layout and parasitic considerations. Different design aspects between these two ZCT inverters are compared and elaborated. The complexity of the 55-kW prototype implementations is compared as well. Efficiencies are measured and compared under a group of torque/speed points for typical EV drive cycles.
Megawatts high-frequency power conversion is another potential application of the ZCT techniques. The integrated gate commutated thyristor (IGCT) device is tested and characterized under the proposed six-switch ZV/ZCT condition, and the test shows promising results in reducing switching losses and stresses. Improvements in the IGCT switching frequency and simplification of the cooling requirements under ZCT operations are discussed. In addition, a generalized ZCT cell concept is developed based on the proposed three-switch ZCT topology. This concept leads to the discovery of a family of simplified multilevel soft-switching inverters that reduce the number of auxiliary switches by half, and still maintain desirable features.Ph. D.
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Jung, Jin Woo. "Modeling and control of fuel cell based distributed generation systems." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1116451881.
Full textAbstract:
Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xvi, 209 p.; also includes graphics. Includes bibliographical references (p. 202-209). Available online via OhioLINK's ETD Center
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Kwak, Sangshin. "Design and analysis of modern three-phase AC/AC power converters for AC drives and utility interface." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2336.
Full textAbstract:
Significant advances in modern ac/ac power converter technologies and demands
of industries have reached beyond standard ac/ac power converters with voltage-source
inverters fed from diode rectifiers. Power electronics converters have been matured to
stages toward compact realization, increased high-power handling capability, and
improving utility interface. Modern ac/ac power converter topologies with various
control strategies have been introduced for the further improvements, such as matrix
converters, current-fed converters, PWM rectifiers, and active power filters. In this
dissertation, several new converter topologies are proposed in conjunction with
developed control schemes based on the modern ac/ac converters which enhance
performance and solve the drawbacks of conventional converters.
In this study, a new fault-tolerant PWM strategy is first proposed for matrix
converters. The added fault-tolerant scheme would strengthen the matrix converter
technology for aerospace and military applications. A modulation strategy is developed
to reshape output currents for continuous operation, against fault occurrence in matrix
converter drives.
This study designs a hybrid, high-performance ac/ac power converter for high
power applications, based on a high-power load commutated inverter and a mediumpower
voltage source inverter. Natural commutation of the load commutated inverter is
actively controlled by the voltage source inverter. In addition, the developed hybrid
system ensures sinusoidal output current/voltage waveforms and fast dynamic response
in high power areas.
A new topology and control scheme for a six-step current source inverter is
proposed. The proposed topology utilizes a small voltage source inverter, to turn off
main thyristor switches, transfer reactive load energy, and limit peak voltages across
loads. The proposed topology maximizes benefits of the constituent converters: highpower
handling capability of large thyristor-based current source inverters as well as fast
and easy control of small voltage source inverters.
This study analyzes, compares, and evaluates two topologies for unity power
factor and multiple ac/ac power conversions. Theoretical analyses and comparisons of
the two topologies, grounded on mathematical approaches, are presented from the
standpoint of converter kVA ratings, dc-link voltage requirements, switch ratings,
semiconductor losses, and reactive component sizes. Analysis, simulation, and
experimental results are detailed for each proposed topology.
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Botterón, Fernando. "Controladores discretos de tensão baseados no princípio do modelo interno aplicados a inversores trifásicos PWM." Universidade Federal de Santa Maria, 2005. http://repositorio.ufsm.br/handle/1/3647.
Full textAbstract:
Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThis thesis contributes to the analysis, project and implementation of discrete-time controllers based on the Internal Model Principle, aiming to improve the performance of three-leg three-phase PWM inverters with insulating output transformer usually found in the output stage of medium power double-conversion UPS. Initially, an investigation about issues concerning to the discrete-time models of three-phase inverters with space vector modulation and the LC filter have been carried out. This investigation shows the impact of different switching sequences, sampling instants and filter cut-off frequency on the harmonic spectrum of sampled variables used for feedback. This is a concern when the switching frequency is low to limit the switching losses as in medium and high power UPS. In this way, this thesis proposes sampling methods that make possible to reduce the low order harmonics on the interest variables, which is relevant when state feedback is used. These methods allow to obtain discrete-time average linear models useful for the controller design. In addition, the saturation of the insulating transformer is addressed in details. The dc component arising from the digital implementation and from the circuit measures non idealities, and then amplified by an inadequate choice of the controller, may lead the transformer to saturate. In order to solve this problem, and in accordance with the Internal Model Principle, internal models adequate to the plant under consideration as well as discrete-time voltage controllers in stationary and synchronous frames which are not prone to amplify the dc component, are proposed. Another goal of this thesis is the improvement of the UPS output voltage transient response due to linear and non linear load steps. This is obtained considering the sampling methods before mentioned, combined with internal models with reduced number of poles and low sampling rate. It is demonstrated that it is possible to improve significantly the output voltage transient responses, as well as to satisfy the rigorous classification of the standard IEC62040-3 for UPS without degrading the steady state performance. In addition, these control structures have enough stability margins, as proved in each case, and they results in simple and attractive solutions to be implemented in 8 or 16 bits fixed-point arithmetic microcontrollers and DSP with reduced memory space. The feasibility of the proposed solutions is verified with experimental results demonstrating both transient and steady-state performances. Finally, a comparative analysis of the proposed control structures, over the light of the standard IEC62040-3, is presented.
A presente tese de doutorado contribui para a análise, projeto e implementação de controladores discretos baseados no Princípio do Modelo Interno, com o intuito de aprimorar o desempenho de inversores trifásicos PWM a três braços com transformador isolador usualmente utilizados no estágio de saída de UPS de dupla conversão de média potência. Inicialmente se realiza uma investigação sobre os aspectos relacionados à obtenção do modelo discreto de inversores trifásicos com modulação space vector e do filtro de saída. Essa investigação mostra o impacto de diferentes seqüências de comutação, instantes de amostragem e freqüência de corte do filtro no conteúdo harmônico das variáveis amostradas usadas para realimentação. Isso é uma preocupação quando a freqüência de comutação é baixa para limitar as perdas em UPS de média e alta potência. Nesse sentido essa tese propõe métodos de amostragem que possibilitam reduzir as harmônicas de baixa ordem nas variáveis de interesse o que adquire importância quando se realiza a realimentação dos estados da planta. Esses métodos permitem a obtenção de modelos médios lineares úteis para o projeto do controlador. Além disso, a saturação do transformador de isolação é analisada em detalhe. A componente contínua oriunda da implementação digital e das não idealidades dos circuitos de medição, e amplificada por uma escolha inadequada do controlador, pode levar o transformador à saturação. Com o intuito de solucionar esse problema, e de acordo com a teoria do Princípio do Modelo Interno, são propostos modelos internos adequados à planta em questão bem como controladores discretos de tensão em eixos estacionários e síncronos, que não tem tendência a amplificar a componente contínua. Outro dos objetivos dessa tese é o aprimoramento da resposta transitória das tensões de saída da UPS na presença de degraus de carga linear e não linear. Isso é obtido considerando-se os métodos de amostragem mencionados acima, combinado com modelos internos com número de pólos e taxa de amostragem reduzidos. Demonstra-se que é possível aprimorar significativamente a resposta transitória das tensões de saída bem como satisfazer a exigente classificação da norma IEC62040-3 para UPS, sem degradar o desempenho de regime permanente. Além disso, essas estruturas de controle possuem suficiente margem de estabilidade, como provado em cada caso, e estas resultam em soluções simples e atrativas para serem implementadas em microcontroladores e DSP de aritmética de ponto fixo, com palavras de 8 e 16 bits e capacidade reduzida de memória. A viabilidade prática das propostas realizadas é verificada com resultados experimentais em regime permanente e transitório. Finalmente, apresenta-se uma análise comparativa das estruturas de controle propostas, sob o enfoque da norma IEC62040-3.
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Aboelhassan, Mustafa Osman Elrayah. "Robustní řízení synchronního stroje s permanentními magnety a spínaným tokem." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2013. http://www.nusl.cz/ntk/nusl-233605.
Full textAbstract:
Je jasné, že nejúspěšnější konstrukce zahrnuje postup vícefázového řízení, ve kterém každá fáze může být považována za samostatný modul. Provoz kterékoliv z jednotek musí mít minimální vliv na ostatní, a to tak, že v případě selhání jedné jednotky ostatní mohou být v provozu neovlivněny. Modulární řešení vyžaduje minimální elektrické, magnetické a tepelné ovlivnění mezi fázemi řízení (měniče). Synchronní stroje s pulzním tokem a permanentními magnety se jeví jako atraktivní typ stroje, jejíž přednostmi jsou vysoký kroutící moment, jednoduchá a robustní konstrukce rotoru a skutečnost, že permanentní magnety i cívky jsou umístěny společně na statoru. FS-PMSM jsou poměrně nové typy střídavého stroje stator-permanentní magnet, které představují významné přednosti na rozdíl od konvenčních rotorů - velký kroutící moment, vysoký točivý moment, v podstatě sinusové zpětné EMF křivky, zároveň kompaktní a robustní konstrukce díky umístění magnetů a vinutí kotvy na statoru. Srovnání výsledků mezi FS-PMSM a klasickými motory na povrchu upevněnými PM (SPM) se stejnými parametry ukazuje, že FS-PMSM vykazuje větší vzduchové mezery hustoty toku, vyšší točivý moment na ztráty v mědi, ale také vyšší pulzaci díky reluktančnímu momentu. Pro stroje buzené permanentními magnety se jedná o tradiční rozpor mezi požadavkem na vysoký kroutící moment pod základní rychlostí (oblast konstantního momentu) a provozem nad základní rychlostí (oblast konstantního výkonu), zejména pro aplikace v hybridních vozidlech. Je předložena nová topologie synchronního stroje s permanentními magnety a spínaným tokem odolného proti poruchám, která je schopná provozu během vinutí naprázdno a zkratovaného vinutí i poruchách měniče. Schéma je založeno na dvojitě vinutém motoru napájeném ze dvou oddělených vektorově řízených napěťových zdrojů. Vinutí jsou uspořádána takovým způsobem, aby tvořila dvě nezávislé a oddělené sady. Simulace a experimentální výzkum zpřesní výkon během obou scénářů jak za normálního provozu, tak za poruch včetně zkratových závad a ukáží robustnost pohonu za těchto podmínek. Tato práce byla publikována v deseti konferenčních příspěvcích, dvou časopisech a knižní kapitole, kde byly představeny jak topologie pohonu a aplikovaná řídící schémata, tak analýzy jeho schopnosti odolávat poruchám.
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Chen, Ching-Chen, and 陳慶臻. "A multicarrier PWM for three-phase four-leg inverter." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/xk4kbd.
Full textAbstract:
碩士中華大學
電機工程學系
106
Three-phase three-leg inverter has an inherent common mode voltage (CMV) problem.Therefore, three-phase four-leg inverter is proposed to mitigate the CMV. This study discusses the characteristics of multicarrier pulse width modulation (PWM) for three-phase four-leg inverter. The analysis of sinusoidal PWM and space vector PWM with multicarrier is presented. The simulation results are utilized to validate the performances of the proposed multicarrier PWM scheme.
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Chang, Chen-Wei, and 張陳維. "A multicarrier PWM for unbalance three-phase four-leg inverter." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/p2a73t.
Full textAbstract:
碩士中華大學
電機工程學系
106
The three-phase four-leg inverter is a system for mitigating common-mode voltages better than three-phase three-arm inverters. Therefore, for the common mode voltage (CMV), two techniques for three-phase four-arm inverters with multi-carrier pulse width modulation (PWM), sinusoidal PWM (SPWM) and space vector PWM (SVPWM) are proposed. To lower the CMV. This method is used to explore the impact on the system under load imbalance. Finally, the experimental and simulation software PSIM platform is used to analyze its system to verify the correctness of the proposed method.
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Huang, Yao-Min, and 黃耀民. "Implementation of the Three-Phase Sine PWM Inverter with DSP-Based." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/45108522869214760245.
Full textAbstract:
碩士聖約翰科技大學
電機工程系碩士班
101
The purpose of this thesis is to develop an independent three-phase AC sine wave power inverter, with maximum load 2.4kW and a voltage modulation rate 4.4%. The control strategy of this power inverter has a PI control with a sinusoidal pulse width modulation by a digital signal processor (TMS320LF2407). The power inverter hardware architecture includes three-phase full bridge architecture, LC filter, and the output voltage feedback input current feedback circuit. Using a high-voltage power supply provide a DC-bus about 320V~350V to convert to 220V/60Hz AC power. This verifies the feasibility of the control theory and design for this inverter connected to the load contained in 2.4kW.
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Somani, Utsav. "Design Optimization of LLC Topology and Phase Skipping Control of Three Phase Inverter for PV Applications." Master's thesis, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6192.
Full textAbstract:
The world is heading towards an energy crisis and desperate efforts are being made to find an alternative, reliable and clean source of energy. Solar Energy is one of the most clean and reliable source of renewable energy on earth. Conventionally, extraction of solar power for electricity generation was limited to PV farms, however lately Distributed Generation form of Solar Power has emerged in the form of residential and commercial Grid Tied Micro-Inverters. Grid Tied Micro-Inverters are costly when compared to their string type counterparts because one inverter module is required for every single or every two PV panels whereas a string type micro-inverter utilizes a single inverter module over a string of PV panels. Since in micro-inverter every panel has a dedicated inverter module, more power per panel can be extracted by performing optimal maximum power tracking over single panel rather than over an entire string of panels. Power per panel extracted by string inverters may be lower than its maximum value as few of the panels in the string may or may not be shaded and thereby forming the weaker links of the system.
In order to justify the higher costs of Micro-Inverters, it is of utmost importance to convert the available power with maximum possible efficiency. Typically, a micro-inverter consists of two important blocks; a Front End DC-DC Converter and Output DC-AC Inverter. This thesis proposes efficiency optimization techniques for both the blocks of the micro-inverter.
This thesis aims to optimize the efficiency of the front end stage by proposing optimal design procedure for resonant parameters of LLC Topology as a Front End DC-DC Converter for PV Applications. It exploits the I-V characteristics of a solar panel to design the resonant parameters such that resonant LLC topology operates near its resonant frequency operating point which is the highest efficiency operating point of LLC Converter.
Due to continuously variable irradiance levels of solar energy, available power for extraction is constantly varying which causes the PV Inverter operates at its peak load capacity for less than 15% of the day time. Every typical power converter suffers through poor light load efficiency performance because of the load independent losses present in a power converter. In order to improve the light load efficiency performance of Three Phase Inverters, this thesis proposes Phase Skipping Control technique for Three Phase Grid Tied Micro-Inverters. The proposed technique is a generic control technique and can be applied to any inverter topology, however, in order to establish the proof of concept this control technique has been implemented on Three Phase Half Bridge PWM Inverter and its analysis is provided. Improving light load efficiency helps to improve the CEC efficiency of the inverter.M.S.E.E.
Masters
Electrical Engineering and Computing
Engineering and Computer Science
Electrical Engineering
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Hu, Chien-Feng, and 胡健峰. "Investigation Into The Effect of Long Lead and Common Mode Voltage for Three Phase PWM Inverter-Fed Induction Motor Drives." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/03064387728705546760.
Full textAbstract:
碩士國立臺灣科技大學
電機工程系
88
This thesis investigates the motor terminal overvoltage, ringing and common-mode voltage in pulse-width modulation (PWM) inverter-fed ac motor drive system where long leads are required. These phenomena may stress the motor winding insulation, and cause shaft voltage, bearing current, and conducted electromagnetic interference (EMI). Premature motor bearing failures and electronic equipment malfunctions have been reported to be directly related to bearing current and EMI. In this paper, parallel resistor, first-order and second-order shunt filter are designed to reduce the overvoltage and ringing at motor terminals, and methods to eliminate common-mode voltage using a three-level sinusoidal PWM inverter are presented. Simulation and experimental results are presented to verify the proposed filter design for 220-V PWM inverter-fed induction motor drive system with 10 meter lead lengths.
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Huynh, Phuoc-Sang, and 黃福尚. "Design and Implementation of an FPGA-Based Digital Current Controller in Applications to Three-Phase PWM Inverters." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/31321744764925582271.
Full textAbstract:
碩士國立交通大學
電機工程學系
102
This thesis presents the design and implementation of an FPGA-based digital current controller, providing a fully integrated solution for high-performance three-phase inverters. The synchronous coordinate current control algorithm is realized with dead-time compensation and one-shunt current sampling by using the introduced controller. First of all, DPWMMIN strategy is employed in the controller under considerations of linear range modulation and switching losses, based on the evaluation of three typical PWM methods, SPWM, SVPWM and DPWMMIN. In the DPWMMIN scheme, the linear modulation range is allowed a 15.5-percent increase in comparison with SPWM. Moreover, on/off switching occurs in only two phase legs each switching cycle, thus the DPWMMIN method introduces less switching losses. Secondly, dead time is required in the standard PWM inverter control to prevent dc-link short circuit. However, this blanking time also results in distortion in output voltage and it becomes quite significant for inverters under low modulation index. A dead-time compensation technique is developed for DPWMMIN. By using the compensation scheme, the width of output voltage pulses is corrected in every switching cycle without position shift. Thirdly, one-shunt current sampling imposes practical implementation challenges for reliable current sensing and low current distortion over wide load variation ranges. Boundary conditions for phase current reconstruction with one-shunt current sensing have been derived from small time intervals of effective voltage vectors. A simple sampling technique is introduced to achieve correct three-phase current information from dc-link current for the DPWMMIN strategy with a minimum of undesirable side effects. Finally, the core of the synchronous coordinate current control algorithm is the coordinate transformation, which needs several multiplications for realization. However, if a dedicated multiplier is used for each multiplication, the cheaper and smaller FPGAs cannot meet the logic resource requirement. To overcome this limitation, a multiplier-sharing strategy is used, which can reduce the number of dedicated multipliers in the FPGA. Experimental verification has been given to illustrate the performance of the proposed controller by using ARM-based mixed-signal FPGA PSOC board, SmartFusion A2F500M3F.
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Ροζίκ, Λυσίμαχος-Ιωάννης. "Προσομοίωση και μελέτη υβριδικού συστήματος διασπαρμένης παραγωγής." Thesis, 2012. http://hdl.handle.net/10889/5430.
Full textAbstract:
Η παρούσα διπλωματική εργασία έχει ως αντικείμενο την μελέτη και τη μοντελοποίηση ενός υβριδικού συστήματος, που αποτελείται από φωτοβολταϊκά και κυψέλες καυσίμου τα οποία τροφοδοτούν ένα μικροδίκτυο. Το φορτίο το οποίο καλείται το σύστημα να καλύψει είναι 30kW και 15kVar. Για τη μοντελοποίηση του συστήματος χρησιμοποιείται το πρόγραμμα σχεδίασης και προσομοίωσης ηλεκτρικών συστημάτων PSCAD.
Στην εργασία αυτή το ενδιαφέρον επικεντρώνεται στη συμπεριφορά του συστήματος στη μόνιμη κατάσταση λειτουργίας και στη συμπεριφορά σε κάποια μεταβατατικά φαινόμενα.
Τα μεταβατικά φαινόμενα που εξετάζονται είναι τα εξής:
- Συμπεριφορά συστήματος σε μεταβολές της ηλιοφάνειας.
- Απόκριση συστήματος σε μεταβολές του φορτίου.
- Τριφασικό και μονοφασικό βραχυκύκλωμα με τη γη στη γραμμή.
Στο κεφάλαιο 1 γίνεται αναφορά στις ανανεώσιμες πηγές, στην εξέλιξή και στην προοπτική τους στο μέλλον. Στη συνέχεια περιγράφονται τα διάφορα είδη των υβριδικών συστημάτων και γίνεται αναφορά για τη διεσπαρμένη παραγωγή και τα μικροδίκτυα.
Στο κεφάλαιο 2 περιγράφεται η λειτουργία των φωτοβολταϊκών κυττάρων, παρουσιάζονται οι I-V και P-V χαρακτηριστικές και στη συνέχεια ακολουθεί αναλυτική περιγραφή του μοντέλου της φωτοβολταϊκής συστοιχίας που θα χρησιμοποιήσουμε στην προσομοίωση στο PScad.
Στο κεφάλαιο 3 περιγράφεται η λειτουργία των κυψελών καυσίμων και παρουσιάζονται τα διάφορα είδη κυψελών που υπάρχουν στις μέρες μας. Εν συνεχεία ακολουθεί αναλυτική περιγραφή της λειτουργίας της κυψέλης καυσίμου πολυμερούς ηλεκτρολυτικής μεμβράνης PEM FC καθώς αυτό το είδος των κυψελών καυσίμου χρησιμοποιούμε στο σύστημά μας. Τέλος, κατασκευάζεται το μοντέλο της PEM FC και ακολουθεί η αναλυτική περιγραφή του μοντέλου.
Στο κεφάλαιο 4 γίνεται αναφορά στους dc/dc μετατροπείς ανύψωσης τάσης και στις περιοχές λειτουργίας τους. Εν συνεχεία γίνεται διαστασολόγηση του ανυψωτή τάσης και παρουσιάζεται το σύστημα ελέγχου του. Επίσης μελετάται η λειτουργία του ανυψωτή ως ανιχνευτή του σημείου μέγιστης ισχύος της φωτοβολταϊκής συστοιχίας και γίνεται προσομοίωση των κυψελών και της φωτοβολταϊκής συστοιχίας με τους dc/dc μετατροπείς που χρησιμοποιούνται.
Στο κεφάλαιο 5 ακολουθεί η περιγραφή της λειτουργίας των μονοφασικών και τριφασικών αντιστροφέων DC/AC και παρουσιάζεται αναλυτικά η στρατηγική της διαμόρφωσης εύρους παλμών (PWM). Τέλος, γίνεται υπολογισμός των τιμών του φίλτρου που τοποθετείται στην έξοδο του αντιστροφέα και στη συνέχεια προσομοιώνεται και μελετάται το μοντέλο του αντιστροφέα που χρησιμοποιούμε στο σύστημά μας.
Στο κεφάλαιο 6 γίνεται η πλήρη προσομοίωση του συστήματος. Περιγράφονται επίσης και τα μοντέλα του φορτίου, του Μ/Σ, του δικτύου και της μηχανής παραγωγής σφαλμάτων. Τέλος, παρουσιάζονται και περιγράφονται τα αποτελέσματα των μελετών που πραγματοποιούνται στο σύστημα (απόκριση συστήματος σε κανονικές συνθήκες, απόκριση συστήματος για μεταβολή της ηλιοφάνειας, μελέτη συστήματος στη μεταβολή του φορτίου, προσομοίωση συστήματος για σφάλματα στη γραμμή).The current diploma thesis presents the study and simulation of a hybrid system, which consists of a Photovoltaic Array (PV) and a Fuel Cell stack (FC), which supports a microgrid. The critical load that the system supports is 30kW and 15kVar. For the system modelling the program of designing and simulation of electric systems PSCAD is used. At this project the interest is focused in the behavior of system in the permanent situation of operation and in the behavior in certain transient phenomena. The transient phenomena that are examined are the following: - Behavior of the system in variations in solar insolation. - System’s response to variations of the load. - Fault analysis (single line to ground and three-phase line to ground short circuit). In Chapter 1 there is a description of renewable energy sources, their development and prospects in the future. Afterwards, the different kinds of hybrid systems are mentioned and there is a reference in distributed generation and microgrids. In Chapter 2 the function of photovoltaic cells and different kinds of photovoltaic technologies are described. Furthermore, I-V and P-V characteristic are presented and then follows an analytical description of the photovoltaic model that we use in our simulation in PScad. In Chapter 3 , the function of the Fuel Cells is described and the different kinds of fuel cells are presented. Afterwards, there is an analytical description of the proton exchange membrane fuel cells (PEM FC) as we use this kind of FC in our system. Finally, the PEM FC model is constructed and an analytical description of the model is made. The Chapter 4 entails information for the dc/dc boost converters and their operating modes. Subsequently the control system of the dc/dc boost converter is presented. Finally, the utilization of the boost converter as a maximum power point tracker is examined and the simulation of the FV and PV with the boost converter is presented. In Chapter 5 there is a description of the function of the single-phase and three-phase dc/ac inverters and the technique of the pulse-width modulation (PWM) is presented. Finally, the value of the output filter of the inverter is calculated and then the model of the dc/ac inverter, which we use in our system, is simulated. In Chapter 6 there is a simulation of the whole system. Furthermore, the models of the load, the transformer and the fault generator are described. Finally, the results of the simulations for which the system was tested is presented (system response to normal conditions, system response to changes in the insolation, System’s response to variations of the load, system response to grid faults).