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.

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.

The parallel active filter (PAF) is the modern solution for harmonic current mitigation and reactive power compensation of nonlinear loads. This thesis is dedicated to detailed analysis, design, control, and implementation of a PAF for a 3- phase 3-wire rectifier load. Specifically, the current regulator and switching ripple filter (SRF) are thoroughly investigated. A novel discrete time hysteresis current regulator with multi-rate current sampling and flexible PWM output, DHCR3, is proposed. DHCR3 exhibits a high bandwidth while limiting the maximum switching frequency for thermal stability and its implementation is simple. In addition to the development of DHCR3, in the thesis state of the art current regulation methods are considered and thoroughly compared with DHCR3. Since the current regulator type determines the SRF topology choice, various SRF topologies are considered and a thorough design study is conducted and SRF topology selection and parameter determination methods are presented via numerical examples. Through a PAF designed for a 10kW diode/thyristor rectifier load, the superior performance of DHCR3 is verified through simulations and experiments and via comparison to other current regulators. The sufficient switching ripple attenuation of the SRF structures for the designed PAF system and the overall performance of the designed and built PAF system are demonstrated via detailed computer simulations and laboratory experiments. This thesis aids the PAF current regulator and SRF selection, design, and implementation.

Series Active Filters (SAF) are designed for harmonic isolation and load voltage regulation of single-phase and three-phase voltage harmonic source type nonlinear loads. The novel Absolute Value Method (AVM) for load voltage harmonic extraction is proposed and applied in the control algorithm of SAF. The SAF compensated systems are represented by simplified linear models such that SAF controller gains can be easily determined. Harmonic isolation and load voltage regulation performances of 2.5 kW single-phase and 10 kW three-phase SAF compensated systems are evaluated by detailed simulations. Laboratory prototype single-phase and three-phase SAFs and loads are designed and manufactured. Digital signal processor based control platform is employed. Exclusive laboratory tests are conducted. Via laboratory experiments and simulations it is shown that AVM yields superior harmonic isolation and load voltage regulation performance compared to the conventional low/high pass filtering method. Theory, simulations, and experiments are well correlated and illustrate the feasibility of the proposed method.

In this thesis, shaft transducerless vector control of Interior Permanent Magnet (IPM) motor with speed and position estimation using saliency based high frequency signal injection and fundamental model based flux observer methods will be investigated. The magnetic saliency characteristic of a 2.2-kW IPM motor will be experimentally extracted by means of high frequency signal injection. High frequency signal injection method will be used to estimate the speed and position at zero and low speed based on the magnetic saliency of the IPM motor. At high speed, fundamental model based flux observer method will be utilized for speed and position estimation. Seamless transition between the two estimation methods will be provided. Using the estimated speed and position information, the motor will be closed loop vector controlled and the drive motion performance over wide speed and load range will be investigated. The IPM motor drive and the estimation/control algorithms will be modeled and their performance will be demonstrated by detailed computer simulations. A three-phase voltage source inverter and a motor test bench will be built, and the estimation/control algorithms will be implemented on a DSP based motor control platform. The IPM motor drive system will be tested in the laboratory and the theory and simulation results will be verified by the experiments.

The study designs and constructs a three-phase to three-phase direct AC&ndash / AC 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.

A voltage source inverter is commonly used to supply a variable frequency variable voltage to a three phase induction motor in a variable speed application. A suitable pulse width modulation (PWM) technique is employed to obtain the required output voltage in the line side of the inverter. Real-time methods for PWM generation can be broadly classified into triangle comparison based PWM (TCPWM) and space vector based PWM (SVPWM). In TCPWM methods such as sine-triangle PWM, three phase reference modulating signals are compared against a common triangular carrier to generate the PWM signals for the three phases. In SVPWM methods, a revolving reference voltage vector is provided as voltage reference instead of three phase modulating waves. The magnitude and frequency of the fundamental component in the line side are controlled by the magnitude and frequency, respectively, of the reference vector. The fundamental line side voltage is proportional to the reference magnitude during linear modulation. With sine-triangle PWM, the highest possible peak phase fundamental voltage is 0.5Vdc, where Vdc is the DC bus voltage, in the linear modulation zone. With techniques such as third harmonic injection PWM and space vector based PWM, the peak phase fundamental voltage can be as high as (formula) (i.e., 0:577Vdc)during linear modulation. To increase the line side voltage further, the operation of the VSI must be extended into the overmodulation region. The overmodulation region extends upto the six-step mode, which gives the highest possible ac voltage for a given (formula). In TCPWM based methods, increasing the reference magnitude beyond a certain level leads to pulse dropping, and gradually leads to six-step operation. However, in SVPWM methods, an overmodulation algorithm is required for controlling the line-side voltage during overmodulation and to achieve a smooth transition from PWM to six-step mode. Numerous overmodulation algorithms have been proposed in the literature for space vector modulated inverter. A well known algorithm among these divides the overmodulation zone into two zones, namely zone-I and zone-II. This is termed as the 'existing overmodulation algorithm' here. This algorithm is modified in the present work to reduce computational burden without much increase in the line current distortion. During overmodulation, the fundamental line side voltage and the reference magnitude are not proportional, which is undesirable from the control point of view. The present work ensures a linear relationship between the two. Apart from the fundamental component, the inverter output voltage mainly consists of harmonic components at high frequencies (around switching frequency and the integral multiples) during linear modulation. However, during overmodulation, low order harmonic components such as 5th, 7th, 11th, 13th etc., are also present in the output voltage. These low order harmonic voltages lead to low order harmonic currents in the motor. The sum of the lower order harmonic currents is termed as 'lower order current ripple'. The present thesis proposes a method for estimation of lower order current ripple in real-time. In closed loop current control, the motor current is fed back to the current controller. During overmodulation, the motor current contains low order harmonics, which appear in the current error fed to the controller. These harmonic currents are amplified by the current error amplifier deteriorating the performance of the drive. It is possible to filter the lower order harmonic currents before being fed back. However, filtering introduces delay in the current loop, and reduces the bandwidth even during linear modulation. In the present work, the estimated lower order current ripple is subtracted from the measured current before the latter is fed back to the controller. The estimation of lower order current ripple and the proposed current control are verified through simulation using MATLAB/SIMULINK and also experimentally on a laboratory prototype. The experimental setup comprises of a field programmable gate arrays (FPGA) based digital controller, an IGBT based inverter and a four-pole squirrel cage induction motor. (Pl refer the original document for formula)

Pulse width modulation (PWM) voltage source converters (VSC) are one type of motor drives that have become popular because they enable precise control of speed and torque in medium voltage motors. However, these drives are known to have adverse effects on the insulation system particularly on conductive armour tape (CAT) and semi-conductive stress grading tape (SGT). These tapes, which are crucial components of the insulation system, control the surface electrical stresses in the stator slot and in the end portion of the form-wound coils outside the grounded stator. The material properties of CAT and SGT and the methods by which they are applied on form-wound motor coils are traditionally designed for power frequency, or a 60 Hz sinusoidal voltage. However, because of the high frequencies associated with the repetition rate and the fast rise time of the PWM pulses, elevated electrical and thermal stresses develop in these tapes, which can lead to premature insulation failure. Little research has been conducted with respect to understanding the mechanism of dielectric heating as a function of frequency and repetitive pulse characteristics. The material characterization of CAT and SGT is a vital part of an investigation of the performance of the stress relief system at high frequencies. In this study, the anisotropic dielectric properties of CAT and SGT have been measured in dc and ac and in low and high electric fields. The laboratory experiments for determining the material characteristics are discussed and the results analyzed. According to the ac space charge limited field (SCLF) theory, the maximum ac tangential component of the electric field in a nonlinear resistive SGT on medium voltage form-wound motor coils can be predicted from the field dependent electrical conductivity and the frequency. However, the SCLF theory cannot predict the total electric field (vector sum of the tangential and normal components) in the air adjacent to the surface of the tapes. Simulations of the electric field using a finite element method (FEM), is one of the best ways of finding the resultant electric field distribution in the air space adjacent to the SGT. However, prior to this study, researchers simplified the modelling of the stress relief system to avoid the convergence problems that develop due to the nonlinearity of the SGT conductivity as a function of the electric field, and also because of the geometry and dimensions of the tapes when their depths are orders of magnitude smaller than the other dimensions associated with form-wound coils. For modelling the stress grading (SG) system at power frequency and at the rated voltage, the dc isotropic conductivity of the SGT and CAT has also been extensively investigated. However, relatively little work has been done with respect to the ac electrical behaviour of these materials and dc modelling cannot reflect the effects of high-frequency stresses on the machine insulation. In this study, comprehensive transient FEM modelling has been developed in order to simulate the insulation system with nonlinear field dependent materials. The actual dimensions of the components are applied in the model, and the appropriate material parameters for the FEM simulations are extracted from the experimental test results. One crucial point that has not been considered in previous studies is the effect of the component of the electric field that is normal to the surface of the coil. In most studies, only the tangential component of the electric field is considered; however, in this study, both components and the resultant electric field are computed. The surface tangential field is calculated with reference to the gradient of the surface potential as measured with an electrostatic voltmeter. It is shown that this technique can provide a reasonable estimate for the tangential field along the SG system, but not without limitations, which are discussed in detail. Based on laboratory work and analytical analysis, this research has successfully determined the relationship between the thermal effect of the PWM voltage and the other repetitive fast pulses, such as square wave and impulse voltages. The influence of the pulse characteristics on the development of stresses has also thoroughly investigated, and the results are presented. A coupled electric and thermal model that incorporates the finite element method (FEM) is used as a means of studying thermal stresses and determining appropriate remedies. However, using transient analysis as an approach for finding the temperature profile associated with high repetitive impulses (1-10 kHz) and fast rise times (~200 ns) is both difficult and impractical. According to these considerations, an alternative method has been developed from stationary analyses based on two sinusoidal voltages of different frequencies. The frequency and amplitude of these sinusoids are measured relative to the switching frequency, signal power, and nonlinearity of the system, and the results of the simulation are then verified experimentally, thus showing the efficacy of this method. This research also concluded that a capacitive SG system with conductive foil embedded in the groundwall insulation can be a practical alternative to a conventional SGT of form-wound coils in inverter fed motors. The performance of the capacitive SG scheme is independent of frequency and can therefore provide the required mitigation of the stress caused by repetitive fast pulses. The results of the evaluation of this system with respect to qualification tests demonstrate the effectiveness of the system.

Η παρούσα διπλωματική εργασία πραγματεύεται τη μελέτη και κατασκευή ενός μετατροπέα για την οδήγηση ενός μονοφασικού επαγωγικού κινητήρα. Η εργασία αυτή εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Σκοπός είναι η μελέτη και κατασκευή ενός τριφασικού αντιστροφέα τάσης για τη λειτουργία και τον έλεγχο των στροφών ενός μονοφασικού επαγωγικού κινητήρα. Αρχικά μελετάται η βασική αρχή λειτουργίας του μονοφασικού επαγωγικού κινητήρα και αναλύονται οι τεχνικές εκκίνησης που χρησιμοποιούνται για σύνδεση του κινητήρα απευθείας στο δίκτυο. Ακόμα παρουσιάζονται τα ισοδύναμα κυκλώματα λειτουργίας του μονοφασικού επαγωγικού κινητήρα, η εξίσωση της ηλεκτρομαγνητικής ροπής του και προσομοιώνεται η λειτουργία του για τη μελέτη της στατικής συμπεριφοράς του. Στη συνέχεια γίνεται μια θεωρητική ανάλυση του κυκλώματος του τριφασικού αντιστροφέα τάσης που κατασκευάστηκε, καθώς και όλων των υπόλοιπων κυκλωμάτων που είναι αναγκαία για τη λειτουργία του. Επιπροσθέτως αναλύεται η μέθοδος παλμοδότησης των διακοπτικών στοιχείων του αντιστροφέα τάσης, που είναι η "Ημιτονοειδής Διαμόρφωση του Εύρους των Παλμών" (SPWM). Στο επόμενο βήμα αναλύονται τα τεχνικά χαρακτηριστικά όλων των κυκλωμάτων που κατασκευάστηκαν, και περιγράφεται ο κώδικας του προγράμματος του μικροελεγκτή, που χρησιμοποιήθηκε για την παραγωγή των παλμών. Τέλος, παραθέτουμε παλμογραφήματα και μετρήσεις που προέκυψαν από τα πειράματα που διενεργήθηκαν μετά την ολοκλήρωση της κατασκευής. / This diploma thesis discourse the analysis and construction of a converter topology for single phase induction motor drives. The project was based in the Laboratory of Electromechanical Energy Conversion of the department of Electrical and Computer Engineering of School Engineering of University of Patras. The objective of this project is the analysis and construction of a three phase voltage inverter to control the speed of a single phase induction motor. The first stage of this work is the study of the basic principle of operation of the single phase induction motor and the analysis of the starting techniques, used for the direct connection to the power grid. The equivalent circuits of the running single phase induction motor and the equation of the electromagnetic torque are also presented in this project. Following, there is a theoretical analysis of the three phase voltage inverter circuit, as well of all the remaining circuit, necessary for its function. Moreover the method of pulse generation for the switching elements of the voltage inverter is analyzed, which is the “Sinusoidal Pulse Width Modulation”. The next step is the analysis of the technical characteristics all of the circuits developed, as well the description of the program code for the microcontroller, used to produce the pulses. Finally oscillograph figures and measurements, occurred from the experiments transacted after the finalization of the construction, are adduced.

Με το πέρασμα των χρόνων, τα συστήματα των ανανεώσιμων πηγών ενέργειας αποκτούν ολοένα και περισσότερο μέρος στα ηλεκτρικά δίκτυα. Το ενεργειακό πρόβλημα καθώς και οι επιπτώσεις στο περιβάλλον που αυτό δημιουργεί, οδηγούν σε εναλλακτικές μεθόδους παραγωγής ηλεκτρικής ενέργειας. Αυτό σημαίνει ότι προστίθονται στο δίκτυο εξαρτήματα τα οποία πρέπει να λειτουργούν αρμονικά το ένα σε σχέση με το άλλο για τον κατάλληλο χειρισμό της ηλεκτρικής ισχύος. Τέτοια εξαρτήματα είναι η μονάδα μετατροπής ενέργειας, ο μετατροπέας, το φίλτρο στην έξοδο του μετατροπέα καθώς και άλλες μονάδες πολύπλοκες ή πιο απλές. Η διακοπτική λειτουργία του μετατροπέα καθώς και η στοχαστική διαδικασία της παραγωγής ηλεκτρικής ενέργειας από τις ανανεώσιμες πηγές, προκαλούν τάσεις και ρεύματα με ανώτερες αρμονικές. Στην παρούσα διπλωματική εργασία θα εξετάσουμε διάφορες μεδόδους ελέγχου ισχύος στην πλευρά του δικτύου, με διάφορους τύπους φίλτρων και φορτίων στην έξοδο του μετατροπέα με σκοπό να εντοπίσουμε τις ομοιότητες και τις διαφορές ανάλογα με την τοπολογία που χρησιμοποιούμε. Τα συστήματα που θα εξομοιώσουμε περιλαμβάνουν την dc διασύνδεση, έναν μετατροπέα ισχύος που λειτουργεί με την μέθοδο PWM, διάφορες τοπολογίες φίλτρων όπως RL, LC και LCL σε ισχυρό δίκτυο και τέλος με διάφορα είδη φορτίων, δηλαδή σε ασθενές δίκτυο. Οι έλεγχοι θα εφαρμοστούν στο dq σύγχρονα στρεφόμενο σύστημα αναφοράς με την συχνότητα του δικτύου, με την βοήθεια του μετασχηματισμού Park έτσι ώστε να ελέγξουμε την dc τάση διασύνδεσης και να επιτύχουμε μοναδιαίο συντελεστή ισχύος από την πλευρά του δικτύου. Τέλος θα προσομοιώσουμε τα παραπάνω συστήματα στο Simulink του Matlab και θα εξάγουμε τα αντίστοιχα συμπεράσματα από τα αποτελέσματα των προσομοιώσεων. / During the years, systems of renewable energy sources are becoming more a significant part of electrical networks. The energy problem and its impact on the environment, lead to alternative methods of electricity production. This means that components added to the network must operate harmoniously in relation one to another for proper handling of electrical power. Such components are the power conversion unit, the inverter, the filter at the output of converter units and other complex or simple devices. The switching operation of the converter and the stochastic process of producing electricity from renewable sources, can provoke voltages and currents of higher harmonic spectrum. In this paper we will examine various methods to control power injected in the utility network with different types of filters and loads on the output of the converter in order to identify similarities and differences depending on the topology used. The systems will include simulation of dc link, a power converter that operates method PWM, different filter topologies such as RL, LC and LCL and then of different load topologies. The control will be applied in modern dq rotating reference system to the grid frequency, making use of the Park transformation to control the dc link voltage and succeed unit power factor in the grid side. In conclusion, simulations of these systems will be done in Simulink of Matlab and conclusions will be drowned.