Current control is an important topic in modern power electronics system. For voltage source inverters, current control loop ensures the waveform quality at steady state and the fast response at transient state. To improve the current control performance, quite a few nonlinear control strategies have been presented and one well-known strategy is the hysteresis current control. It achieves fast response without stability issue and it has high control precision. However, for voltage source inverter applications, hysteresis current control has a wide switching frequency range, which introduces additional switching loss and impacts the design of harmonic filter. Other nonlinear current control strategies include one-cycle control, non-linear carrier control, peak current control, charge control, and so on. However, these control strategies are just suitable for specific topologies and it cannot be directly used by voltage source inverters. The recently proposed parabolic current control solves the frequency variation problem of hysteresis current control by employing a pair of parabolic carriers as the control band. By the use of parabolic current control, approximate-constant switching frequency can be achieved. Due to the cycle-by-cycle control structure, it inherently has fast response speed and high precision. These advantages make it suitable for voltage source inverters, including stand-alone inverters, grid connected inverters, active power filters, and power factor correction applications. However, parabolic current control has some limitations, such as dead-time effects, only working as bipolar PWM, complex hardware implementation, non-ideal converging speed. These problems are respectively solved in this dissertation and solutions include dead-time compensation, the implementation on dual-carrier unipolar PWM, sensorless parabolic current control, single-step current control. With the proposed dead-time compensation strategy, current control precision is improved and stable duty-cycle range are extended. Dual-carrier PWM implementation of parabolic current control has smaller harmonic filter size and lower power loss. Sensorless parabolic current control decreases the cost of system and enhances the noise immunity capability. Single-step current control pushes the convergence speed to one switching operation with simple implementation. High switching frequency is allowed and power density can be improved. Detailed analysis, motivation and experimental verification of all these innovations are covered in this dissertation. In addition, the duality phenomenon exists in electrical circuits, such as Thevenin's theorem and Norton's theorem, capacitance and inductance. These associated pairs are called duals. The dual of parabolic current control is derived and named parabolic voltage control. Parabolic voltage control solves the audible noise problem of burst mode power converters and maintains high efficiency in the designed boost converter. / Ph. D. / Current control strategy is an important topic in power converter design. Good current control strategy helps to control the quality of input or output waveform of power conversion systems. This dissertation studied an attractive current control strategy named parabolic current control. Parabolic current control solves some drawbacks of conventional current control strategies with enhanced performance. However, it still has some application limitations. This dissertation proposed four new strategies to solve the application limitations of parabolic current control. Motivated by the duality phenomenon, a voltage control strategy named parabolic voltage control is also proposed, serving as the dual of parabolic current control. By the use of parabolic voltage control, audible noise in some power conversion systems can be eliminated and conversion efficiency can be ensured. All these new ideas in this dissertation are carefully derived in theory and verified by experimental test results.

Η παρούσα διπλωματική εργασία πραγματεύεται την μελέτη και κατασκευή ενός συστήματος ελέγχου για έναν κινητήρα μαγνητικής αντίδρασης (Reluctance). Η εργασία αυτή εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών της πολυτεχνικής σχολής του Πανεπιστημίου Πατρών. Σκοπός της εργασίας αυτής, είναι η μελέτη και η κατασκευή ενός τριφασικού αντιστροφέα πηγής τάσης, ο οποίος θα επιτρέπει την υλοποίηση βαθμωτού και διανυσματικού ελέγχου για έναν σύγχρονο κινητήρα μαγνητικής αντίδρασης χωρίς έκτυπους πόλους στο στάτη. Ο σύγχρονος κινητήρας μαγνητικής αντίδρασης χωρίς έκτυπους πόλους στο στάτη, όπως και οποιοσδήποτε άλλος κινητήρας μαγνητικής αντίδρασης, βασίζει τη λειτουργία του στη ροπή αντίδρασης, γεγονός από το οποίο προέρχεται και η ονομασία των κινητήρων αυτού του είδους (ReluctanceMotors). Το κύριο χαρακτηριστικό των κινητήρων μαγνητικής αντίδρασης είναι η έλλειψη οποιασδήποτε πηγής διέγερσης στο δρομέα. Τα τελευταία χρόνια έχει αναπτυχθεί έντονο επιστημονικό ενδιαφέρον σχετικά με τη βελτιστοποίηση της κατασκευής των σύγχρονων κινητήρων μαγνητικής αντίδρασης χωρίς έκτυπους πόλους στο στάτη, καθώς και των μεθόδων ελέγχου, που μπορούν να εφαρμοστούν για βελτιστοποίηση της λειτουργίας τους. Αρχικά μελετήθηκαν οι βασικές αρχές λειτουργίας των μηχανών εναλλασσόμενου ρεύματος και η ανάλυση επικεντρώθηκε στο σύγχρονο κινητήρα μαγνητικής αντίδρασης. Μελετήθηκαν τα κατασκευαστικά χαρακτηριστικά του σύγχρονου κινητήρα μαγνητικής αντίδρασης χωρίς έκτυπους πόλους στο στάτη, το μαθηματικό μοντέλο που περιγράφει τη λειτουργία του, συγκρίθηκε με άλλους τύπους κινητήρων εναλλασσόμενου ρεύματος και παρουσιάστηκαν οι μέθοδοι ελέγχου που μπορούν να εφαρμοστούν σε έναν σύγχρονο κινητήρα μαγνητικής αντίδρασης χωρίς έκτυπους πόλους στο στάτη. Επιπλέον μελετήθηκε ο τριφασικός αντιστροφέας πηγής τάσης, ο οποίος είναι απαραίτητος για την οδήγηση ενός σύγχρονου κινητήρα μαγνητικής αντίδρασης, καθώς και διάφορες τεχνικές για την παλμοδότησή του. Τέλος προσομοιώθηκε ο σύγχρονος κινητήρας μαγνητικής αντίδρασης με το πρόγραμμα προσομοίωσης Matlab/Simulink για διάφορες καταστάσεις λειτουργίας του, και ακολούθησε η κατασκευή του τριφασικού αντιστροφέα για την πειραματική διερεύνηση και επιβεβαίωση των αποτελεσμάτων της προσομοίωσης. / The present diploma thesis deals with the design and manufacture of a control system for a Reluctance Motor. This work was developed in the Laboratory of Electromechanical Energy Conversion at the Department of Electrical Engineering and Computer Technology of the School of Engineering in the University of Patras, Greece. The purpose of this thesis is the design and manufacture of a three-phase voltage source inverter for the control of the performance of a Synchronous Reluctance Motor by the implementation of Scalar and Vector control. The operation of Synchronous Reluctance Motor, like any other type of Reluctance Motors, is based on reluctance torque. The main characteristic of Reluctance Motors is that the rotor does not have any field winding. During the last years, a great interest has emerged around the Synchronous Reluctance Motor, which mainly focuses on the optimization of its construction and control. At first, an introduction to the operation principles of the AC motor is done, while the main interest is focused on Synchronous Reluctance Motor. The analysis of Synchronous Reluctance Motor covers many aspects, such as its construction characteristics, its dynamic model, its control strategies, as well as a comparison with other AC motors. Furthermore the three phase inverter is studied and its modulation techniques, since it is used for the driving of the motor. Finally the Synchronous Reluctance Motor is simulated in Matlab/Simulink for some operating conditions, and a three phase voltage source inverter is constructed for the experimental investigation and to see the relationship between the results of the simulation and the experiment.

Este trabalho, constitui-se em uma contribuição para o estudo das estratégias de mo-dulação direta baseadas em histerese e que funcionam em frequência fixa de comutação. Tem como objetivo principal propor a estratégia delta modificada, que diferencia-se na forma de ajuste da largura de banda de histerese, alterando-se seus limites e em como executa o comando de bloqueio das chaves de potência, para que a corrente de saída se mantenha em frequência fixa de operação e apresente rápida resposta dinâmica no sistema controlado. Para tanto, não necessita da utilização de derivadas, nem de uma corrente média de referência, tão pouco, se utiliza dos tempos de comutação. A estratégia proposta, comprova que é possível produzir os adequados pulsos de comando para o processamento da energia proveniente de célula combustível, através do conversor estático de potência, utilizando-se, principalmente, dos valores de ultrapassagem nos limites estabelecidos de histerese. Como objetivo secundário desta pesquisa, desenvolve-se um conversor CC/CC auxiliar para adaptar e estabilizar a energia proveniente da CAC, compondo-se um sistema útil que serve de base para fornecer energia, aos mais diversos tipos de cargas em CC. Além disso, apresenta-se uma revisão das estratégias de modulação em modo direto para o controle da corrente de saída no conversor estático, tendo como base a tensão nos terminais de um indutor. Contudo, outras estratégias são naturalmente citadas, no transcorrer deste trabalho, devido haver combinações entre as diferentes estratégias moduladoras e controladoras comentadas. / This work, is a contribution to the study of direct modulation strategies based on hysteresis and that operate at fixed switching frequency. Its main objective is to propose the modified delta strategy, which differentiates from the others strategies in the form of adjustment of hysteresis bandwidth, changing its limits and in executing the locking command of the power keys, so that the output current is maintain at fixed frequency of operation and a rapid dynamic response in the controlled system. In order to do so, it does not require the use of derivatives or a reference average current and also the switching times are not used. This strategy shows that it is possible to produce the appropriate command pulses for the processing of fuel cell energy by the static power converter using mainly the exceedance limit values. As a secondary objective of this research, an auxiliary DC/DC converter is developed to adapt and stabilize the energy coming from the fuel cell, forming a useful system that serves as a base to supply power to the most diverse types of DC loads. In addition, we present a review of the direct-mode modulation strategies for the control of the output current in the static converter, updating data, and based on the voltage at the terminals of an inductor; how-ever, others strategies are naturally cited because there are combinations between the different modulating strategies and controllers commented on in the course of this work.

Neste trabalho é apresentado o desenvolvimento de um sistema de ensaios elétricos de dispositivos de emissão de campo para que, a partir desses ensaios, possam ser extraídas as características elétricas desses dispositivos. O sistema é composto por hardware e software dedicados e pode ser controlado local ou remotamente. O hardware inclui uma fonte de alta tensão gerenciada por um sistema microcontrolado. Para programação do microcontrolador, foi utilizado um ambiente de programação disponibilizado pelo próprio fabricante do microcontrolador. Nesse desenvolvimento foram empregados periféricos de entrada e saída do microcontrolador, tais como: leitura de teclado, manipulação de USART, ajuste do nível de saída da fonte e conversores analógicos digitais. No microcontrolador foram implantadas rotinas de configuração, personalização e varredura do display, além de envio e recebimento de informações com um computador. Para o computador foi elaborado um programa dedicado para a manipulação do sistema de ensaio utilizando o conceito de instrumentação virtual, que permite escolher o tipo de ensaio elétrico, armazenar as leituras dos ensaios e a visualização \"on-line\" do andamento do ensaio através de diversos gráficos disponíveis no programa, inclusive o gráfico de Fowler-Nordheim, adequado para o estudo de dispositivos de emissão de campo. / At this work is presented the development of a field emission devices trial system to render possible to obtain the electrical characteristics of the field emission devices. Here are shown some results taken from some trials. During the development of the trial system, it was used at the programming microcontroller stage, the environment of programming supplied by the manufacturer of the microcontroller. At this development, peripheral of input and output from the microcontroller, like, keyboard reading, USART manipulation, SPI manipulation and analogic to digital converters were used. At the microcontroller were implanted routines of configuration, customing and display sweeping, besides the transmission and the receiving of instructions came from the computer. For computer, a program was elaborated dedicated for manipulation of the trials system applying the virtual instrumentation concept, storing readings of the trials as well as the visualization \"on-line\" of the course of the trial through available graphs in the program. As an important result of this work has the establishment of a system for trial of field emission devices controlled on place or remotely, system that is composed by hardware and software in which were made several trials with acquisition and data manipulation and the presentation of received information.

Neste trabalho é apresentado o desenvolvimento de um sistema de ensaios elétricos de dispositivos de emissão de campo para que, a partir desses ensaios, possam ser extraídas as características elétricas desses dispositivos. O sistema é composto por hardware e software dedicados e pode ser controlado local ou remotamente. O hardware inclui uma fonte de alta tensão gerenciada por um sistema microcontrolado. Para programação do microcontrolador, foi utilizado um ambiente de programação disponibilizado pelo próprio fabricante do microcontrolador. Nesse desenvolvimento foram empregados periféricos de entrada e saída do microcontrolador, tais como: leitura de teclado, manipulação de USART, ajuste do nível de saída da fonte e conversores analógicos digitais. No microcontrolador foram implantadas rotinas de configuração, personalização e varredura do display, além de envio e recebimento de informações com um computador. Para o computador foi elaborado um programa dedicado para a manipulação do sistema de ensaio utilizando o conceito de instrumentação virtual, que permite escolher o tipo de ensaio elétrico, armazenar as leituras dos ensaios e a visualização \"on-line\" do andamento do ensaio através de diversos gráficos disponíveis no programa, inclusive o gráfico de Fowler-Nordheim, adequado para o estudo de dispositivos de emissão de campo. / At this work is presented the development of a field emission devices trial system to render possible to obtain the electrical characteristics of the field emission devices. Here are shown some results taken from some trials. During the development of the trial system, it was used at the programming microcontroller stage, the environment of programming supplied by the manufacturer of the microcontroller. At this development, peripheral of input and output from the microcontroller, like, keyboard reading, USART manipulation, SPI manipulation and analogic to digital converters were used. At the microcontroller were implanted routines of configuration, customing and display sweeping, besides the transmission and the receiving of instructions came from the computer. For computer, a program was elaborated dedicated for manipulation of the trials system applying the virtual instrumentation concept, storing readings of the trials as well as the visualization \"on-line\" of the course of the trial through available graphs in the program. As an important result of this work has the establishment of a system for trial of field emission devices controlled on place or remotely, system that is composed by hardware and software in which were made several trials with acquisition and data manipulation and the presentation of received information.

In this thesis, design and implementation of a distribution-type, voltage source converter (VSC) based static synchronous compensator (D-STATCOM) having the simplest converter and coupling transformer topologies have been carried out. The VSC STATCOM is composed of a +/- 750 kVAr full-bridge VSC employing selective harmonic elimination technique, a low-pass input filter, and a &amp / #8710 / /Y connected coupling transformer for connection to medium voltage bus. The power stage of VSC based STATCOM is composed of water-cooled high voltage IGBT modules switched at 850 Hz for the elimination of 5th, 7th, 11th, 13th, 17th, 19th, 23rd,and 25th voltage harmonics. Special care has been taken in the laminated busbar design to minimize stray inductances between power semiconductors and dc link capacitor. Reactive power control is achieved by applying the phase angle control technique. The effect of input filter on total demand distortion has been investigated theoretically by mathematical derivations. The proposed VSC STATCOM has been implemented for reactive power compensation of Coal Preparation System in Kemerk&ouml / y Thermal Power Plant. The field test results have shown the success of the implemented system in view of fast response in reactive power compensation, and minimum input current harmonic content, and compliance with the IEEE Std. 519-1992 even for the weakest power systems. The application of selective harmonic elimination technique and phase angle control to VSC STATCOM has led to optimum switching frequency and device utilization for high voltage IGBTs at the expense of slower response as compared to other PWM techniques.

<p>This project deals with voltage source converters with energy storage capability. The main objective is to study the possible benefits of energy storage to a power system with a VSC as the interface between them.</p><p>First of all, a converter control system is proposed for a two level VSC. In the conventional converter control, the control system usually takes the voltage measured at the point where the converter is connected and calculates the reference voltage for the converter; with a modulation system the converter then produces the required 'average voltage'. In this project, a novel flux modulation scheme, combined with the deadbeat current control strategy, is proposed. The current controller is capable of controlling both positive and negative sequence current components. With flux modulation, the control system measures the bus flux and commands the converter to generate the required flux.</p><p>Based on the proposed control strategies, several application studies have been carried out.</p><p>The first application study investigates the effect of energy storage on the power quality at the point of common coupling when a system is subject to load disturbances. The voltage at PCC in a weak network is very sensitive to load changes. A sudden change in active load will cause both a phase jump and a magnitude fluctuation in the bus voltage, whereas reactive load changes mainly affect the voltage magnitude. With the addition of energy storage to a StatCom, it is possible to compensate for the active power change as well as providing reactive power support. In this thesis, some effective active power compensation schemes are proposed. Simulations and experiments have been performed to verify the compensation schemes. The results show that a StatCom with energy storage can significantly reduce phase jumps and magnitude deviations of the bus voltage.</p><p>pact of the energy storage on the performance of weak systems under fault conditions has been investigated. The investigation was done by studying an example system. The system model was established based on a real system, in which some induction motors driving pumps along a pipeline are fed from a radial transmission line. Studies show that for a weak system with induction motor loads, a StatCom with certain energy storage capacity will effectively improve the system recovery after faults. Although this incurs extra cost for the increasing dc voltage rating and size of the dc side capacitor, the overall rating of the converter can be reduced by utilization of the proposed active power compensation scheme.</p><p>The last case study investigates the possible use of a StatCom with energy storage to improve the power quality at the point of common coupling where a cyclic load is connected. Studies show that by providing both fast reactive and fast active power support to the network, not only the voltage magnitude can be well controlled, but also the voltage phase jump can be reduced significantly.</p>

Οι συνεχώς αυξανόμενες ενεργειακές απαιτήσεις της σύγχρονης κοινωνίας σε συνδυασμό με τις ραγδαίες κλιματικές αλλαγές μας οδηγούν στην ανάγκη παραγωγής ηλεκτρικής ενέργειας με όσο το δυνατό πιο οικονομικό και φιλικό προς το περιβάλλον τρόπο. Έτσι, οι Ανανεώσιμες Πηγές Ενέργειας αποκτούν ολοένα και μεγαλύτερο μερίδιο στην παραγωγή ηλεκτρικής ενέργειας, αλλάζοντας συνεχώς τον παγκόσμιο ενεργειακό χάρτη. Τα αιολικά συστήματα, τα οποία αξιοποιούν την κινητική ενέργεια του ανέμου, είναι ένα είδος ΑΠΕ. Στην παρούσα εργασία μελετάμε ένα αιολικό σύστημα, το οποίο αποτελείται από μία ανεμογεννήτρια μεταβλητών στροφών που χρησιμοποιεί μία σύγχρονη μηχανή μόνιμου μαγνήτη, έναν μετατροπέα πηγής τάσης, ένα R-L φίλτρο στην πλευρά του δικτύου και μία γραμμή μεταφοράς μικρού μήκους. Η αυξημένη αξιοπιστία και απόδοση της ΣΜΜΜ την καθιστούν ιδιαίτερα ελκυστική λύση για τα αιολικά συστήματα. Στην εργασία αυτή προσομοιώνουμε σε περιβάλλον Matlab/Simulink το σύστημα που περιγράψαμε παραπάνω. Εφαρμόζοντας τις κατάλληλες τεχνικές ελέγχου από την πλευρά της μηχανής προσπαθούμε να πετύχουμε μέγιστη απομάστευση ισχύος από τον άνεμο, ενώ στην πλευρά του δικτύου προσπαθούμε μέσω άμεσου ελέγχου ροής ισχύος να πετύχουμε μοναδιαίο συντελεστή ισχύος με ταυτόχρονη ρύθμιση της τάσης της dc διασύνδεσης. Στη συνέχεια, μέσω ενός πρόσθετου ελέγχου προσπαθούμε να κρατήσουμε την τάση στην έξοδο του φίλτρου σταθερή, κατά τη διάρκεια πτώσης της τάσης του δικτύου. Τέλος, παραθέτουμε τα αποτελέσματα της προσομοίωσης μαζί με έναν σύντομο σχολιασμό και τα συμπεράσματα. / The continuously increasing energy requirements of modern society combined with the rapid climate changes lead us to the need to produce electrical energy in a more economic and environmentally friendly way. Thus, the Renewable Energy Sources gain an increasing share of electrical energy production, constantly changing the global energy map. Wind power systems, which utilize the kinetic energy of the wind, are a kind of RES. In this thesis we study a wind power system, which comprises a variable speed wind turbine, which uses a permanent magnet synchronous machine, a voltage source converter, an R-L filter in the grid side and a short transmission line. The increased reliability and performance of PMSG make it particularly attractive solution for wind power systems. In this thesis we simulate in Matlab/Simulink environment the system described above. Applying appropriate control techniques on the machine side we try to achieve maximum power harvesting from the wind, while on the grid side we try through direct power flow control to achieve unit power factor with simultaneous control of the dc link voltage. Then, using an additional control we try to keep constant the voltage at the end of the R-L filter during a grid voltage drop. Finally, we present the simulation results along with a brief commentary and the conclusions.

A new concept, the multi level voltage/current reinjection ac/dc conversion, is described in this thesis. Novel voltage and current source converter configurations, based on voltage and current reinjection concepts are proposed. These converter configurations are thoroughly analyzed in their ac and dc system sides. The fundamentals of the reinjection concept is discussed briefly, which lead to the derivation of the ideal reinjection waveform for complete harmonic cancellation and approximations for practical implementation. The concept of multi level voltage reinjection VSC is demonstrated through two types of configurations, based on standard 12-pulse parallel and series connected VSC modified with reinjection bridges and transformers. Firing control strategies and steady state waveform analysis are presented and verified by EMTDC simulations. The multi level current reinjection CSC is also described using two configurations based on standard 12-pulse parallel and series connected CSC modified with associated reinjection circuitry. Firing control strategies and steady state waveform analysis are presented and verified by EMTDC simulations. Taking the advantage of zero current switching in the main bridge valves, achieved through multi level current reinjection, an advanced multi level current reinjection scheme, consisting thyristor main bridges and self-commutated reinjection circuitry is proposed. This hybrid scheme effectively incorporates self-commutated capability into a conventional thyristor converter. The ability of the main bridge valves to commutate without the assistance of a turn-off pulse or line commutating voltage under the zero current condition is explained and verified by EMTDC simulations. Finally, the applications of the MLCR-CSC are discussed in terms of a back to back HVDC link and a long distance HVDC transmission system. The power and control structures and closed loop control strategies are presented. Dynamic simulation is carried out on PSCAD/EMTDC to demonstrate the two systems ability to respond to varying active and reactive power operating conditions.

The McTronX research group, at the Potchefstroom campus of the North–West University, has been researching Active Magnetic Bearings (AMBs). A fully suspended, flywheel energy storage system (FESS) has been developed. Due to excessive unbalance on the rotor, the motor drive could not be tested up to its rated speed. In the interim, until the rotor can be balanced and other rotor dynamic effects have been investigated, the group decided that the existing drive control should be improved and tested on a high–speed permanent magnet synchronous motor (PMSM), using normal roller element bearings. In order to test the motor control a second (identical) PMSM, mechanically coupled to the former, operates in generator mode which serves as the torque load. Two different control algorithms, namely V/f and vector control, are designed and implemented on a rapid control prototyping system, i.e. dSPACE®. The V/f control is an open–loop, position sensorless technique, whilst the vector controller makes use of a position sensor. From the design and implementation it became clear that the vector control is more robust, in the sense that it is less sensitive on parameter variations and disturbances. It can start up reliably even under full load conditions. The V/f control is an attractive alternative to the vector control, especially in AMB systems, where it may be difficult to mount the position sensor, has to operate in a hazardous environment not suited to the sensor or could degrade the reliability of the AMB system. The cost of the position sensor is not really a concern compared to the cost of an AMB system. The V/f control is more suited to fan and pump applications, which has a low dynamic requirement. The V/f control has high startup currents and is not recommended for applications requiring a high starting torque or fast acceleration during operation. The inverter, which drives the PMSM, also had to be developed. With regard to the motor control, the effects of inverter non–idealities had to be accounted, especially for the V/f control. The implemented control algorithms were tested up to 20 krpm. Discrepancies between the expected and actual results are discussed. Overall, the controllers performed as desired. Generally, the project goals have been reached satisfactorily. / Thesis (M.Ing. (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2011.