This thesis attempts to investigate the performance of various reactive power compensation devices, examine the mechanism of reactive power compensation for HVDC systems, and develop guidelines for the design of reactive power compensation schemes for HVDC systems. The capabilities of various reactive power compensators to enhance power system stability are compared in both steady and transient states. An understanding of the capabilities of these compensators provides a basis for further investigation of their performance in HVDC systems. The reactive power requirements of HVDC converters are studied. The voltage dependencies of the HVDC converters at different control modes are derived, which allow for predictions of how HVDC converters impact AC system voltage stability. The transient performance of reactive power compensation options for HVDC Systems is studied by comparing their behavior during DC fault recovery, Temporary Overvoltage (TOV), and commutation failure. How to quantify the system strength when reactive compensators are connected to the converter bus is investigated. A new series of indices are developed based on the Apparent Short Circuit Ratio Increase (ASCRI). The inertia of a synchronous condenser and its impact on the frequency stability of an AC/DC system are discussed. By modelling the inverter side AC system in greater detail, the frequency stability and rotor angle stability following fault transients is examined based on time domain simulation. Finally, a guideline for designing dynamic reactive power compensation for HVDC systems is proposed.

This thesis attempts to investigate the performance of various reactive power compensation devices, examine the mechanism of reactive power compensation for HVDC systems, and develop guidelines for the design of reactive power compensation schemes for HVDC systems. The capabilities of various reactive power compensators to enhance power system stability are compared in both steady and transient states. An understanding of the capabilities of these compensators provides a basis for further investigation of their performance in HVDC systems. The reactive power requirements of HVDC converters are studied. The voltage dependencies of the HVDC converters at different control modes are derived, which allow for predictions of how HVDC converters impact AC system voltage stability. The transient performance of reactive power compensation options for HVDC Systems is studied by comparing their behavior during DC fault recovery, Temporary Overvoltage (TOV), and commutation failure. How to quantify the system strength when reactive compensators are connected to the converter bus is investigated. A new series of indices are developed based on the Apparent Short Circuit Ratio Increase (ASCRI). The inertia of a synchronous condenser and its impact on the frequency stability of an AC/DC system are discussed. By modelling the inverter side AC system in greater detail, the frequency stability and rotor angle stability following fault transients is examined based on time domain simulation. Finally, a guideline for designing dynamic reactive power compensation for HVDC systems is proposed.

Σε κάθε Σύστημα Ηλεκτρικής Ενέργειας η ηλεκτρική ισχύς έχει δύο συνιστώσες: Την ενεργό, η οποία σχετίζεται με το παραγόμενο έργο και την άεργο, η οποία δε σχετίζεται με την παραγωγή έργου, αλλά συνεισφέρει σε απώλειες και πτώση τάσεως. Για να αποφύγουμε αυτά τα αρνητικά, στοχεύουμε στη μείωση της αέργου ισχύος, επιτυγχάνοντας έτσι βελτίωση του συντελεστή ισχύος. Με την πάροδο του χρόνου, τα επίπεδα αρμονικών τάσεων και ρευμάτων αυξάνονται συνεχώς, δημιουργώντας έντονα προβλήματα στα Συστήματα Ηλεκτρικής Ενέργειας. Λαμβάνοντας υπ’ όψιν στην ανάλυση ροής ισχύος ενός κυκλώματος την επίδραση των ανώτερων αρμονικών τάσης και ρεύματος, η βελτίωση του συντελεστή ισχύος γίνεται πολύπλοκη διαδικασία, ειδικά στην περίπτωση μη ιδανικής πηγής (μη μηδενική εσωτερική σύνθετη αντίσταση). Σκοπός της διπλωματικής εργασίας είναι η αναζήτηση τεχνικών περιορισμού της αέργου ισχύος, αφού πρώτα συσχετισθεί με τις ανώτερες αρμονικές τάσεως και ρεύματος. Γενικά, το πρόβλημα περιγράφεται και αναλύεται με διάφορες θεωρίες ισχύος και λύνεται με την τοποθέτηση κυκλωμάτων που επιτυγχάνουν αντιστάθμιση της αέργου ισχύος. Αρχικά αναφέρεται η περίπτωση βελτίωσης του συντελεστή ισχύος θεωρώντας ιδανική πηγή (μηδενική εσωτερική σύνθετη αντίσταση) με ημιτονοειδή τάση εξόδου και γραμμικό φορτίο. Σε αυτή την απλή περίπτωση, ένας πυκνωτής είναι ικανός να αντισταθμίσει πλήρως την καταναλούμενη από το φορτίο άεργο ισχύ. Στη συνέχεια εξετάζονται τα περιθώρια βελτίωσης του συντελεστή ισχύος σε συστήματα με: • Ιδανική, μη ημιτονοειδή πηγή τροφοδοσίας και γραμμικό φορτίο • Μη ιδανική, μη ημιτονοειδή πηγή τροφοδοσίας και γραμμικό φορτίο Στην πρώτη περίπτωση, η τοποθέτηση απλά ενός πυκνωτή παράλληλα προς το φορτίο μπορεί να βελτιώσει το συντελεστή ισχύος του φορτίου μέχρι ενός σημείου, ο οποίος λαμβάνει εν γένει τιμές μικρότερες της μονάδας. Υπάρχει δυνατότητα βελτίωσης του συντελεστή ισχύος μέχρι και τη μονάδα, χρησιμοποιώντας έναν πιο πολύπλοκο αντισταθμιστή. Στην πρώτη αυτή περίπτωση, η τιμή του αντισταθμιστή μπορεί να βρεθεί και αναλυτικά, ενώ στη δεύτερη περίπτωση η τιμή του πυκνωτή αντιστάθμισης υπολογίζεται μόνο με τη βοήθεια ενός επαναληπτικού αλγορίθμου. / In any power system electrical power has two components: active, which is related to the work done and reactive, which is not associated with the production of work, but contribute to losses and voltage drop. To avoid these negative, we aim to reduce reactive power, thus improving the power factor. Over time, the levels of harmonic voltages and currents are growing, creating severe problems in power systems. Considering the power flow analysis of a circuit the influence of higher harmonic voltage and current, improving the power factor is a complex process, especially in the case of non-ideal source (non-zero internal impedance). The purpose of this thesis is to find mitigation techniques reactive power, after having been associated with higher voltage and current harmonics. Generally, the problem is described and analyzed with various theories of power and is solved by placing circuits achieve reactive power compensation. Initially, the case for improving the power factor assuming ideal source (zero internal impedance) with sinusoidal output voltage and linear load. In this simple case, a capacitor is able to compensate fully consumed by the load reactive power. Then examine the scope for improving the power factor systems: • Ideal, non-sinusoidal power and linear load • Not ideal, non-sinusoidal power and linear load In the first case, the simple placement of a capacitor in parallel to the load can improve the power factor of the load up to a point, which generally takes values ​​smaller unit. Is it possible to improve the power factor up to the unit, using a more complex equalizer. In the first case, the value of the compensator can be found analytically, while in the second case the value of the compensation capacitor is calculated only using an iterative algorithm.

This thesis report describes the modeling procedure for available the wind turbine generator (WTG) technologies. The models are generic in nature and manufacturer independent. These models are implemented on commercially available dynamic simulation software platforms like PSCAD/EMTDC and MATLAB/SIMULINK. A brief introduction to the available WTG types is provided to understand the technological differences and their key features. The related theoretical concepts to the working of a WTG are explained, which acts as an aid for model development and implementation. Using the theoretical concepts as basis, a WTG model is divided into four parts : 1. Aerodynamic model 2. Mechanical drive train model 3. Electrical machine model 4. Controller model Once the different parts of a WTG are introduced, a groundwork for model implementation on the software platforms is laid. A step-by-step process of implementing a PSCAD or MATLAB model of a WTG is introduced in this thesis. Starting with the most fundamental WTG technology such as fixed-speed also known as direct-connect wind turbine. The model implementation is adanvced to other superior technology like the dynamic rotor resistance control (DRR) and the doubly-fed induction generator (DFIG). To better understand the working of a DFIG, a current-source regulated model (without electrical machine) emulating the DFIG is built on both PSCAD and MATLAB. A full blown converter model of the DFIG with back-to-back converter is then built in PSCAD/EMTDC. An approach to determine the reactive power capability (Q limits) of a DFIG is described. Rotor current limitation and stator current limitation of the DFIG are considered in determining the minimum and maximum reactive power delievered by the DFIG. Variation in the Q limits of a DFIG for change in wind speed is analysed with two different wind speed scenarios. 1. Wind speed from cut-in to rated i.e. 6 m/s - 14 m/s. 2. Wind speed above rated to cut-out i.e. 14 m/s - 20 m/s. Such an analysis, is useful in determining the operating mode of the DFIG. At low wind speeds (below rated), the DFIG can be operated as a STATCOM for exporting and importing reactive power (similar to synchronous machines). While above rated wind speeds, the DFIG can be set to produce maximum active power. Using the DFIG current-source model implemented in MATLAB/SIMULINK, laboratory experiments to plot the power profile of the DFIG is explained. Another experiment to perform independent P-Q control of the DFIG is also included in this report. / text

Este trabalho propõe uma metodologia para enumerar soluções, que indiquem a barra e a compensação de potência reativa necessária para o sistema elétrico sob análise, que atendam aos requisitos avaliados pela função objetivo e as restrições. Nessa alocação de compensação ótima de potência reativa, obtemos as melhores barras e configurações de potências e tecnologias de dispositivos de compensação, minimizando as perdas totais de potência ativa da rede. Em redes fracas com conversores de frequência (por exemplo, para conexão de fontes renováveis, ou interligações utilizando conversores HVDC), esta metodologia proposta busca a melhor relação de curto-circuito trifásico (SCR) no ponto de conexão do conversor de frequência, melhorando a conexão da barra de interesse. O método busca soluções para alocar um único dispositivo de compensação, e soluções alocando simultaneamente dois dispositivos. A metodologia proposta baseia-se na enumeração exaustiva das soluções, e o estudo de caso nos sistemas de 14 e 30 barras do IEEE mostrou a aplicabilidade e funcionalidade da metodologia proposta. / This work proposes a methodology to enumerate solutions, which indicate the bar and the reactive power compensation required for the electrical system under analysis, that meet the requirements evaluated by the objective function and the constraints. In this allocation of optimal compensation of reactive power, we obtain the optimal bars and technologies of compensation devices, minimizing the total losses of active power of the network. In weak networks with frequency converters (e.g. for connection of renewable sources, or interconnections using HVDC converters), the proposed methodology seeks the best threephase short-circuit (SCR) relation at the connection point, improving the connection of the new generation. The method looks for solutions to allocate a single compensation device, and solutions to allocate two devices simultaneously. The proposed methodology is based on the exhaustive enumeration of the solutions. A case study carried out in the IEEE 14 and 30 bus systems shows the applicability and performance of the proposed methodology.

The most important advantages of Multilevel Inverters are the absence of a coupling transformer for medium voltage applications and low harmonic current content. In this way, relocatable and economical STATCOM systems can be realized. Complex control algorithms and the isolation problems of measurement devices and power supplies are the main challenging parts of this type of application. In this study, the design, realization, and the performance of a Voltage Source Type Cascaded Multilevel Converter Based STATCOM will be investigated in terms of digital computation, control hardware and the semiconductors devices commercially available in the market. This research work is fully supported by the Public Research Grant Committee (KAMAG) of TUBiTAK within the scope of National Power Quality Project of Turkey with the project No: 105G129.

Distribution system voltage and VAR control (VVC) is a technique that combines conservation voltage reduction and reactive power compensation to operate a distribution system at its optimal conditions. Coordinated VVC can provide major economic benefits for distribution utilities. Incorporating distributed generation (DG) to VVC can improve the system efficiency and reliability. The first part of this dissertation introduces a direct optimization formulation for VVC with DG. The control is formulated as a mixed integer non-linear programming (MINLP) problem. The formulation is based on a three-phase power flow with accurate component models. The VVC problem is solved with a state of the art open-source academic solver utilizing an outer approximation algorithm. Applying the approach to several test feeders, including IEEE 13-node and 37-node radial test feeders, with variable load demand and DG generation, validates the proposed control. Incorporating renewable energy can provide major benefits for efficient operation of the distribution systems. However, when the number of renewables increases the system control becomes more complex. Renewable resources, particularly wind and solar, are often highly intermittent. The varying power output can cause significant fluctuations in feeder voltages. Traditional feeder controls are often too slow to react to these fast fluctuations. DG units providing reactive power compensation they can be utilized in supplying voltage support when fluctuations in generation occur. The second part of this dissertation focuses on two new approaches for dual-layer VVC. In these approaches the VVC is divided into two control layers, slow and fast. The slow control obtains optimal voltage profile and set points for the distribution control. The fast control layer is utilized to maintain the optimal voltage profile when the generation or loading suddenly changes. The MINLP based VVC formulation is utilized as the slow control. Both local reactive power control of DG and coordinated quadratic programming (QP) based reactive power control is considered as the fast control approaches. The effectiveness of these approaches is studied with test feeders, utility load data, and fast-varying solar irradiance data. The simulation results indicate that both methods achieve good results for VVC with DG.

Η παρούσα διπλωματική εργασία πραγματοποιήθηκε κατά το διάστημα 11/2011-9/2012 στα πλαίσια των ερευνητικών δραστηριοτήτων του εργαστηρίου Παραγωγής, Μεταφοράς, Διανομής και Χρησιμοποίησης Ηλεκτρικής Ενέργειας του τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών του Πανεπιστημίου Πατρών, υπό την επίβλεψη του καθηγητή Γαβριήλ Β. Γιαννακόπουλου. Σκοπός της εργασίας είναι η σύγκριση της δυναμικής συμπεριφοράς ενός συμβατικού σύγχρονου αντισταθμιστή και ενός εγκάρσιου στατικού αντισταθμιστή αέργου ισχύος (SVC) σε ένα εγκατεστημένο ηλεκτρικό δίκτυο, προσομοιώνοντας διαφορετικές περιπτώσεις που επηρεάζουν την διαδικασία αντιστάθμισης αέργου ισχύος και υποστήριξης τάσης σε ζυγούς του δικτύου. Στην εργασία αυτή παρουσιάζονται το μαθηματικό μοντέλο του σύγχρονου αντισταθμιστή, οι επαγωγικές παράμετροι που το χαρακτηρίζουν, τα διαφορετικά μοντέλα συστημάτων διέγερσης που χρησιμοποιούνται και ο Μετασχηματισμός Park. Όσον αφορά τον εγκάρσιο στατικό αντισταθμιστή (SVC) παρουσιάζονται οι βασικές αρχές ελέγχου των TCR και TSC που διαθέτει, η χαρακτηριστική τάσης-ρεύματος και γίνεται μια αναλυτική περιγραφή των συνιστωσών του συστήματος ελέγχου του, όπως ο ρυθμιστής τάσης, το σύστημα συγχρονισμού και η γεννήτρια παραγωγής παλμών. Τέλος, για την μοντελοποίηση και την προσομοίωση των αντισταθμιστών και του ηλεκτρικού δικτύου χρησιμοποιείται το πρόγραμμα PSCAD/EMTDC λόγω της αξιοπιστίας και της ευχρηστίας του σε μεγάλος εύρος ενεργειακών μελετών. / The current thesis was held during the period 11/2011-9/2012 within the research activities of the Generation, Transmission, Distribution and Utilization of Electric Energy Laboratory, Department of Electrical and Computer Engineering, University of Patras, under the supervision of Professor Gabriel B. Giannakopoulos. The purpose of this study is to compare the dynamic performance of a conventional synchronous condenser and a static reactive power compensator (SVC) on an installed electrical grid, simulating different cases affecting the process of reactive power compensation and voltage support at the network’s load buses. This thesis includes representation of the mathematical model of the conventional synchronous condenser and the inductive parameters that characterize it, the different excitation system models used and the Park Transformation. Regarding the static VAR compensator (SVC), this thesis also refers to the fundamentals of TCR and TSC control, the explanation of the current-voltage characteristic and the analytic description of the control system’s components, such as the voltage regulator, the synchronization system and the gate-pulse generator. Lastly, for the modeling and simulation of both compensators and the installed electrical grid, the simulation program used is PSCAD / EMTDC because of its usability and reliability on a wide range of energy projects.

Este trabalho propõe uma metodologia para enumerar soluções, que indiquem a barra e a compensação de potência reativa necessária para o sistema elétrico sob análise, que atendam aos requisitos avaliados pela função objetivo e as restrições. Nessa alocação de compensação ótima de potência reativa, obtemos as melhores barras e configurações de potências e tecnologias de dispositivos de compensação, minimizando as perdas totais de potência ativa da rede. Em redes fracas com conversores de frequência (por exemplo, para conexão de fontes renováveis, ou interligações utilizando conversores HVDC), esta metodologia proposta busca a melhor relação de curto-circuito trifásico (SCR) no ponto de conexão do conversor de frequência, melhorando a conexão da barra de interesse. O método busca soluções para alocar um único dispositivo de compensação, e soluções alocando simultaneamente dois dispositivos. A metodologia proposta baseia-se na enumeração exaustiva das soluções, e o estudo de caso nos sistemas de 14 e 30 barras do IEEE mostrou a aplicabilidade e funcionalidade da metodologia proposta. / This work proposes a methodology to enumerate solutions, which indicate the bar and the reactive power compensation required for the electrical system under analysis, that meet the requirements evaluated by the objective function and the constraints. In this allocation of optimal compensation of reactive power, we obtain the optimal bars and technologies of compensation devices, minimizing the total losses of active power of the network. In weak networks with frequency converters (e.g. for connection of renewable sources, or interconnections using HVDC converters), the proposed methodology seeks the best threephase short-circuit (SCR) relation at the connection point, improving the connection of the new generation. The method looks for solutions to allocate a single compensation device, and solutions to allocate two devices simultaneously. The proposed methodology is based on the exhaustive enumeration of the solutions. A case study carried out in the IEEE 14 and 30 bus systems shows the applicability and performance of the proposed methodology.

Orientador: Dionizio Paschoareli Junior / Banca: Falcondes Jose Mendes de Seixas / Banca: Hari Bruno Mohr / Resumo: A tendência dos sistemas de energia elétrica é uma operação cada vez mais próxima de seus limites operacionais. A presença de equipamentos que utilizam a eletrônica de potência, no controle e condicionamento da energia, é cada vez mais freqüente. A utilização de conversores como fonte de tensão, associados a elementos armazenadores de energia como, por exemplo, a bateria de sódio-enxofre, com alta densidade de energia, alta eficiência na carga e descarga e ainda um longo ciclo de vida, é a configuração básica de um Compensador Regenerativo de Potência Ativa. Compensação regenerativa de potência é um conceito que permite o armazenamento de energia em períodos favoráveis sob o ponto de vista dos custos da energia elétrica. Este conceito de compensação baseia-se no armazenamento da energia excedente ao longo do dia, nos períodos de menor tarifação, para utilizá-la nos horários de ponta (sobre-tarifa), aproveitando-se as vantagens contratuais de consumo de energia fora de ponta e promovendo-se uma melhor equalização de consumo, permitindo uma redução no contrato de demanda. Portanto, na compensação regenerativa de potência ativa, os períodos de consumo de energia são deslocados, com o objetivo de se obter redução na tarifa. Este conceito mostra-se interessante em sistemas com tarifação do tipo horo-sazonal, como é o caso brasileiro. Com o objetivo de se verificar tal troca de potência ativa, um modelo trifásico foi implementado e simulado. Os controles da potência ativa trocada entre o compensador e o sistema e da tensão na barra na qual o mesmo está instalado são realizados independentes e por controladores do tipo PID. Os sinais de controle dos interruptores semicondutores que compõe o conversor como fonte de tensão são gerados a partir do DSP TMS320F2808 da Texas Instruments, o que está embarcado no módulo didático eZdsp F2808 da Spectrum Digital / Abstract: Nowadays, electric power systems are expected to work closer to their operating limits. Power electronics based controllers, such as voltage sourced converters, are increasingly present in power systems. Electronic devices are often used to energy controlling and conditioning. The use of voltage sourced converters, associated to high-density storage elements, is the basic configuration of a Regenerative Active Power Compensator. Regenerative Active Power Compensator is a concept which proposes the energy storage as a possibility for revaluation of electrical energy cost with demand contracts. This concept is based on storing energy surplus during off peak periods, when the energy cost is cheaper, and injecting it back to the system during the overpriced peak periods. This procedure allows a better equalization of energy consumption and a reduction in electric power demand contracts. Therefore, using regenerative active power compensation, the consumption is dislocated from peak periods, resulting in a reduction of energy costs for the consumer. This concept is especially attractive for countries that use hour-seasonal fees police, as in the Brazilian case. This work proposes a three-phase model simulation with digital signal processor controller to investigate the active power flow control between the power system and the compensator, using a proportional-integral-derivative control strategy. The control signals are generate using the Texas Instruments DSP TMS320F2808, witch is embedded into the eZdsp F2808 didactic module, from Spectrum Digital / Mestre