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>

Η παρούσα διπλωματική ασχολείταιμε τις σύγχρονες μεθόδους που εφαρμόζονται στα συστήματα ηλεκτρικής ενέργειας για την βελτίωση των χαρακτηριστικών τους χρησιμοποιώντας αφενός τις τεχνολογικές εξελίξεις στον τομέα των ημιαγωγικών διακοπτικών στοιχείων και αφετέρου την εγκατεστημένη θεωρία ελέγχου. Στο κεφάλαιο 1 επιχειρείται μια εισαγωγή στις έννοιες των συστημάτων μεταφοράς ηλεκτρικής ενέργειας (ΣΗΕ) καθώς και στην αρχή λειτουργίας τους.Στη συνέχεια γίνεται αναφορά στην έννοια της ποιότητας ισχύος και στα προβλήματα που παρουσιάζονται στα ηλεκτρικά δίκτυα. Τέλος αναφέρονται τα προβλήματα εκείνα που με την πάροδο του χρόνου έκαναν επιτακτική την εισχώρηση της τεχνολογίας των ηλεκτρονικών ισχύος στο πεδίο τους και ιδιαίτερα στην κατεύθυνση της αντιστάθμισης αέργου ισχύοςπου αποτελεί ένα απο τα κυριότερα προβλήματα. Στο κεφάλαιο 2 συνεχίζουμε αναλύοντας τη μορφή που παίρνουν τα σύγχρονα ΣΗΕ μετά την είσοδο της τεχνολογίας των FACTS ξεκινώντας από τα θυρίστορ ,ηλεκτρονικούς διακόπτες ισχύος,που αποτελούν δομικά στοιχεία των νέων διατάξεων και επόμενα τις γενικότερες διατάξεις που χρησιμοποιούνται στα ΣΗΕ που συνδυάζουν τα νέα στοιχεία ακόμα και με τους μηχανικούς διακόπτες που ήταν ο προηγούμενος τρόπος ελέγχου των ΣΗΕ. Στο κεφάλαιο 3 γίνεται μια πιο ενδελεχή αναφορά στα κυκλώματα τεχνολογίας ηλεκτρονικών ισχύος που χρησιμοποιύνται ώστε να πάρουν μορφή οι προηγούμενες διατάξεις ,ξεκινώντας από τη βασική μονάδα του μετατροπέα ημιγέφυρας δομικό στοιχείο των DC/AC μετατροπέων.Ακόμα στο κεφάλαιο αυτό αναφερόμαστε στον έλεγχοτων διατάξεων ,αναλύοντας τα συστήματα αναφοράς και τις τεχνικές που υπάρχουν για να καταστεί δυνατή η οδήγησή τους. Στο κεφάλαιο 4 τα πράγματα γίνονται πιο συγκεκριμένα και αναφερόμαστε στο στατικό αντισταθμιστή (STATCOM).Παρουσιάζονται τα κυκλώματα ελέγχου που περιέχει έτσι ώστε να γίνεται δυνατός ο έλεγχος τάσης είτε διάφορες άλλες δυνατότητες που μπορεί να προσφέρει στο πλαίσιο της καλύτερης λειτουργίας των σύγχρονων ΣΗΕ.Επίσης αναπτύσσεται το μαθηματικό και δυναμικό μοντέλο με τις εξισώσεις στα βήματα του οποίου θα κινηθεί και η προσομοίωση του επόμενου κεφαλαίου. Στο κεφάλαιο 5 γίνεται προσομοίωση της λειτουργίας του στατικού αντισταθμιστή και παρουσιάζονται διάφορα διαγράμματα από τα επιμέρους κυκλώματα που αναδεικνύουν τη λειτουργία του.Κύριο αντικείμενο και εδώ αποτελεί η θεωρία ελέγχου και ιδιαίτερη μνεία γίνεται στην χρησιμοποίηση των PI ελεγκτών εκείνω οι οποίοι ρυθμίζουν παραμέτρους του συστήματος και μετουσιώνουν τη μετάβαση από τα παλαιότερα συστήματα που χρησιμοποιούνταν στα ΣΗΕ όπως ο έλεγχος με μηχανικούς διακόπτες. Στο κεφάλαιο 6 τέλος προχωράμε σε κάποιες ιδέες και προτάσεις για μελλοντική έρευνα ως αποτέλεσμα της ενασχόλησης με την συγκεκριμένη διπλωματική εργασία. / In capter 1 there is an intoduction to the Electrical Power Systems terminology,as well as their function and principles.Next,the meaining of power quality is presented along with the problems that occur at the electrical main grids.More emphsis is given to the ones that gradually enforced the use power electronics for reactive power compensation. In chapter 2,an analysis is made about the form of the modern Electrical Power Systems after the development of the FACT technology,starting from thyristors ,electronic power switches,which are elementsof the new layout and continuing with other modern devices which combine these new elements even with the old mechanical switches. In chapter 3,the electronic power systems' circuits are examined more thorouglyin order to understand the layout of the aforementioned structures,starting from the elementary unit of the half bridge power converter.Moreover,the control of these structures is examined,analyzing the reference systems and the various techniques in order to drive them. Chapter 4, presents the static compensator (STATCOM) along with its control circuits.In addition, the mathematical and dynamic model is developed, forming equations where the simulation of the next chapter is based. In chapter 5,there is a simulation of STATCOM's function (in MATLAB software) and various diagrams are presented showing different variables during its operation.Main purpose of this section is the presentation of the control theory,highlighting the use of PI controllers which adjust the system's parameteres and realize the transition from the older structures used in Electrical Power Systems ,such us mechanical switching. In chapter 6,we present some ideas in terms of future survey as a result of our dealing with the certain thesis

The focus of this research is on deriving small signal stability models for different Flexible AC Transmission Systems devices by introducing a simple systematic method that is applicable to any dynamic device. Two different small signal models for Unified Power Flow Controllers are introduced. One model is called the power control mode and the other model is the voltage control mode. The two models are compared from transient stability point of view to show the necessity of developing both models for UPFC. The thesis also shows how to derive the small signal stability model of Static Synchronous Compensator, as the shunt branch of UPFC. The small signal stability models of both devices are then validated to ensure the accuracy of the derived models. STATCOM and UPFC power control mode are validated against PSCAD. The UPFC voltage control mode is validated against nonlinear solution of system equations.

This thesis presents a comprehensive procedure to study sub-synchronous interactions in wind integrated power systems effectively and efficiently. The proposed procedure involves a screening phase and a detailed analysis phase. The screening is performed using a frequency scan and the detailed analysis is performed using small signal stability analysis. To facilitate the small signal analysis, a detailed linearized model of a Type 3 wind power plant is presented in this thesis. The model presented includes the generator, a three-mass drive train model, rotor and grid side converter controller models, converter transformer model and the pitch controller model. To accurately capture the effects of sub-synchronous interactions, the ac network is modelled using dynamic phasors. It is shown that using the proposed procedure, the sub-synchronous interaction between a Type 3 wind power plant and a series compensated line is due to an electrical resonance between the wind power plant generator and the series capacitor. It is also shown that this interaction is highly controllable through the rotor side converter current controllers. This fact will be proven by studying the sub-synchronous interactions in a single machine power system as well as in multi machine power systems. This thesis also presents a sub-synchronous interaction mitigation method using network devices. The performance of an SVC and a STATCOM is evaluated in this thesis. A small signal stability analysis based method will be used to design a sub-synchronous damping controller. A method will be presented to estimate the damping controller parameters systematically to obtain the desired performance using small signal stability analysis results. Furthermore, it will be shown that by strongly controlling the voltage of the point of common coupling, the damping of the oscillations produced by the sub-synchronous interaction between the wind power plant and the series compensated line can be improved. Based on the findings of this research, the thesis proposes a number of recommendations to be adopted when studying the sub-synchronous interactions in wind integrated power systems. These recommendations will facilitate to do such studies effectively and pinpoint the root cause of the sub-synchronous interactions.

The focus of this research is on deriving small signal stability models for different Flexible AC Transmission Systems devices by introducing a simple systematic method that is applicable to any dynamic device. Two different small signal models for Unified Power Flow Controllers are introduced. One model is called the power control mode and the other model is the voltage control mode. The two models are compared from transient stability point of view to show the necessity of developing both models for UPFC. The thesis also shows how to derive the small signal stability model of Static Synchronous Compensator, as the shunt branch of UPFC. The small signal stability models of both devices are then validated to ensure the accuracy of the derived models. STATCOM and UPFC power control mode are validated against PSCAD. The UPFC voltage control mode is validated against nonlinear solution of system equations.

Orientador: Percival Bueno de Araujo / Banca: Carlos Roberto Minussi / Banca: Laurence Duarte Colvara / Banca: Roberto Apolonio / Banca: Vivaldo Fernando da Costa / Resumo: Este trabalho apresenta estudos referentes à inclusão do dispositivo FACTS STATCOM e a utilização de Redes Neurais Artificiais para o ajuste dos parâmetros de sinais adicionais estabilizantes (PSS's e POD's) no sistema de potência multimáquinas. O objetivo é a melhoria da estabilidade frente às pequenas perturbações do sistema de energia elétrica. O modelo matemático utilizado para o estudo das oscilações eletromecânicas de baixa freqüência em sistemas de energia elétrica foi o Modelo de Sensibilidade de Potência (MSP), modificado para permitir a inclusão do dispositivo STATCOM. Este modelo baseia-se no princípio de que o balanço de potência ativa e reativa deve ser satisfeito continuamente em qualquer barra do sistema durante um processo dinâmico. Prosseguindo na realização do trabalho foram desenvolvidos os modelos matemáticos para a inclusão dos PSS's e POD's no sistema elétrico, bem como foi realizada uma discussão a respeito da escolha do local de instalação destes controladores e técnicas clássicas para o ajuste de seus parâmetros. A partir disto foram utilizadas redes neurais artificiais (RNA's) com o objetivo de ajustar os parâmetros dos controladores. A rede utilizada para este fim foi a do tipo Perceptron Multicamadas, sendo utilizado para o seu treinamento o algoritmo Backpropagation. Simulações foram realizadas e os resultados obtidos para os sistemas testes Sul Brasileiro, Simétrico de Duas Áreas e New England são comentados / Abstract: This work presents studies about the inclusion of FACTS STATCOM devices using neural networks tune stability additional signal parameters (PSS's and POD's) on a multi-machine power system. The objective is to improve the stability to small perturbations in electric power systems. The mathematical model used for studying the lower frequency electromechanical oscillations is the Power Sensitivity Model (PSM), modified to allow the inclusion of the STATCOM device. This model is based on the principle that the active and reactive power balance must be continuously satisfied in every bus of the system during the dynamical process. Mathematical models were developed to include the PSS's and POD's on the electrical system, as well as the local to install these control devices and the classical techniques to adjust these parameters. Afterwards, the neural networks were used to adjust the parameters of the controllers. The neural network used is a Perceptron Multi Layer, with the training by backpropagation. Simulations were effectuated for the South Brazilian Power System, the Two Areas Symmetrical Power System and the New England Power System / Doutor

Orientador: Percival Bueno de Araujo / Resumo: Neste trabalho é desenvolvido o modelo matemático de sistemas elétricos de potência multimáquinas para avaliar a estabilidade a pequenas perturbações, com a atuação simultânea de diferentes dispositivos FACTS controlando o fluxo de potência. Os FACTS do tipo SSSC e STATCOM são modelados, considerando suas perdas internas, o modelo resultante é acrescentado à resolução do fluxo de potência, considerando que cada dispositivo FACTS controla uma grandeza do sistema. Utilizando da solução do fluxo, das matrizes Ybarra e Jacobiana, e também tensões e potências, estes são empregados ao Modelo de Sensibilidade de Potência, por meio de simulações, é verificada a atuação dos elementos de controle na estabilidade a pequenas perturbações de sistemas multimáquinas. Para acréscimo de amortecimento às oscilações eletromecânicas, são aplicados controladores ESP e POD. A partir da representação de espaço de estados do modelo final, os autovalores resultantes são estudados para avaliar a estabilidade do sistema. Ao final é discutida a atuação individual e conjunta dos dispositivos FACTS na estabilidade, quando aplicados ao controle do fluxo de potência. / Abstract: In this work the mathematical model of multi-machine power electric systems is developed to evaluate the stability to small perturbations, with the simultaneous actuation of different FACTS devices controlling the power flow. The FACTS of type SSSC and STATCOM are modeled, considering their internal losses, the resulting model is added to the resolution of the power flow, considering that each FACTS device controls a quantity of the system. By the solution of the power flux, the Ybus and Jacobian matrices, as well as voltages and powers, these are used to the Power Sensitivity Model, by means of simulations, it is verified the performance of the control elements in the stability to small perturbation of multi-machine systems. For addition of damping to electromechanical oscillations, ESP and POD controllers are applied. From the state space representation of the final model, the resulting eigenvalues are studied to evaluate the stability of the system. At the end, the individual and combined performance of the FACTS devices in the stability, when applied to the control of the power flow, is discussed. / Doutor

Orientador: Percival Bueno de Araujo / Banca: Anna Diva Plasencia Lotufo / Banca: Igor Kopcak / Resumo: Este trabalho apresenta estudos referentes à modelagem do dispositivo FACTS STATCOM para posterior inclusão nas equações do Modelo de Sensibilidade de Potência multimáquinas. O objetivo final da modelagem é o estudo da estabilidade a pequenas perturbações de sistemas elétricos de potência. São considerados dois modelos para o dispositivo: um primeiro modelo permite apenas a compensação de potência reativa, enquanto que num segundo modelo é possível a compensação tanto de potência ativa como de potência reativa. Também são sugeridos controladores para o dispositivo FACTS STATCOM e, neste trabalho, estes controladores são descritos por blocos de primeira ordem. Com o equacionamento do sistema elétrico realizado, seu modelo é implementado computacionalmente para se efetuar simulações para se avaliar a estabilidade a pequenas perturbações. As simulações estão baseadas na análise no domínio do tempo e no domínio da frequência, utilizando os dois modelos desenvolvidos para o STATCOM. A partir dos resultados obtidos pelas simulações, análises são realizadas, e discutidos os principais aspectos referentes à estabilidade a pequenas perturbações de sistemas elétricos de potência / Abstract: This work presents studies referred to the modeling of the FACTS STATCOM device to include in multi-machine Power Sensitivity Model equations. The aim is to study electrical system stability under small perturbations. Two models are considered for the device: the first one allows only the reactive power compensation, while the other one allows the reactive or active compensation. Controllers for the FACTS STATCOM device are also suggested, and in this work they are described by first order blocks. As the electrical system equations are finalized, the model is computationally implemented to effectuate simulations and evaluate the stability under small perturbations. The simulations are based on the time and frequency domain using the two models developed for the FACTS STATCOM device. Considering the results obtained by the simulations the analysis are realized and discussed the principal aspects referred to the electrical Power system stability under small perturbations / Mestre

Variable renewable energy sources are today increasingly integrated in the power system as a step towards the renewable society. The large-scale introduction of converter-based energy sources brings challenges in terms of reduced damping to the power system due to the reduced number of synchronous generators. This can be manifested as high rate-of-change-of-frequency and decreased grid stability. To forestall this reduced performance, it is suggested that the grid-following control of today’s converters are restructured to a grid-forming control, enabling the converter to behave closer to a synchronous machine.   This thesis compares grid-following and grid-forming control and seeks to further describe this grid-forming behavior by applying a grid-forming control method on an energy storage enhanced STATCOM-system. A continuous time model and a linearized model based on state space representations are constructed in order to investigate the grid-forming behavior but also how the converter stability is affected by a restructure from grid-following to grid-forming control.   The results indicate that the investigated grid-forming control method displays a behavior similar to synchronous machines and incorporates the ability to provide frequency response services and so called “synthetic inertia” to the grid.  The results also show that the stability of the converter (the ability to provide a bounded output when the system is perturbed) is ensured when the control method is restructured from grid-following to grid-forming and that the investigated grid-forming method is stable also in weak grid situations.