Power systems are critical infrastructures for the society. They are therefore planned and operated to provide a reliable eletricity delivery. The set of tools and methods to do so are gathered under security management and are designed to ensure that all operating constraints are fulfilled at all times. During the past decade, raising awareness about issues such as climate change, depletion of fossil fuels and energy security has triggered large investments in wind power. The limited predictability of wind power, in the form of forecast errors, pose a number of challenges for integrating wind power in power systems. This limited predictability increases the uncertainty already existing in power systems in the form of random occurrences of contingencies and load forecast errors. It is widely acknowledged that this added uncertainty due to wind power and other variable renewable energy sources will require new tools for security management as the penetration levels of these energy sources become significant. In this thesis, a set of tools for security management under uncertainty is developed. The key novelty in the proposed tools is that they build upon probabilistic descriptions, in terms of distribution functions, of the uncertainty. By considering the distribution functions of the uncertainty, the proposed tools can consider all possible future operating conditions captured in the probabilistic forecasts, as well as the likeliness of these operating conditions. By contrast, today's tools are based on the deterministic N-1 criterion that only considers one future operating condition and disregards its likelihood. Given a list of contingencies selected by the system operator and probabilitistic forecasts for the load and wind power, an operating risk is defined in this thesis as the sum of the probabilities of the pre- and post-contingency violations of the operating constraints, weighted by the probability of occurrence of the contingencies. For security assessment, this thesis proposes efficient Monte-Carlo methods to estimate the operating risk. Importance sampling is used to substantially reduce the computational time. In addition, sample-free analytical approximations are developed to quickly estimate the operating risk. For security enhancement, the analytical approximations are further embedded in an optimization problem that aims at obtaining the cheapest generation re-dispatch that ensures that the operating risk remains below a certain threshold. The proposed tools build upon approximations, developed in this thesis, of the stable feasible domain where all operating constraints are fulfilled. / <p>QC 20150508</p>

A single-phase, buck-boost based, dual-output AC-DC converter is studied in this thesis. The converter has two DC outputs with opposite polarities, which share the same ground with the input power line. The power stage performance, including the input filter, is studied and procedure to select power components is given. The circuit model is analyzed to develop appropriate control. Zerocrossing distortion of the source input current is addressed and a solution is proposed. Experimental results are satisfactory in that a high power factor line current results for steady-state operation.

This thesis presents an application of the Ant Colony algorithm for optimizing filter placement and sizing on a radial distribution system to reduce power losses and keep the effective harmonic voltage values and the total harmonic distortion (THD) within prescribed limits. First, a harmonic load flow (HLF) algorithm is performed to demonstrate the effect of harmonic sources on total power loss. Then the Ant Colony algorithm is used in conjunction with HLF to place a selection of filter sizes available at each possible location so that both power loss and THD are minimized. As a result the optimal adjustment of location and size of the filter are determined. Results of computational experiments on standard test systems are presented to demonstrate improvement and effectiveness of using the filters at the optimal location. The methodology used can be easily extended to different distribution network configurations. / Master Thesis

An increased penetration of renewable energy into the electric power grid is desirable from an environmental standpoint as well as an economical one. However, renewable sources such as wind and solar energy are often variable and intermittent, and additionally, are non-dispatchable. Also, the locations with the highest amount of available wind or solar may be located in areas that are far from areas with high levels of demand, and these areas may be under the control of separate, individual entities. In this dissertation, a method that coordinates these areas, accounts for the variability and intermittency, reduces the impact of renewable energy forecast errors, and increases the overall social benefit in the system is developed. The approach for the purpose of integrating intermittent energy sources into the electric power grid is considered from both the planning and operations stages. In the planning stage, two-stage stochastic optimization is employed to find the optimal size and location for a storage device in a transmission system with the goal of reducing generation costs, increasing the penetration of wind energy, alleviating line congestions, and decreasing the impact of errors in wind forecasts. The size of this problem grows dramatically with respect to the number of variables and constraints considered. Thus, a scenario reduction approach is developed which makes this stochastic problem computationally feasible. This scenario reduction technique is derived from observations about the relationship between the variance of locational marginal prices corresponding to the power balance equations and the optimal storage size. Additionally, a probabilistic, or chance, constrained model predictive control (MPC) problem is formulated to take into account wind forecast errors in the optimal storage sizing problem. A probability distribution of wind forecast errors is formed and incorporated into the original storage sizing problem. An analytical form of this constraint is derived to directly solve the optimization problem without having to use Monte-Carlo simulations or other techniques that sample the probability distribution of forecast errors. In the operations stage, a MPC AC Optimal Power Flow problem is decomposed with respect to physical control areas. Each area performs an independent optimization and variable values on the border buses between areas are exchanged at each Newton-Raphson iteration. Two modifications to the Approximate Newton Directions (AND) method are presented and used to solve the distributed MPC optimization problem, both with the intention of improving the original AND method by improving upon the convergence rate. Methods are developed to account for numerical difficulties encountered by these formula- tions, specifically with regards to Jacobian singularities introduced due to the intertemporal constraints. Simulation results show convergence of the decomposed optimization problem to the centralized result, demonstrating the benefits of coordinating control areas in the IEEE 57- bus test system. The benefit of energy storage in MPC formulations is also demonstrated in the simulations, reducing the impact of the fluctuations in the power supply introduced by intermittent sources by coordinating resources across control areas. An overall reduction of generation costs and increase in renewable penetration in the system is observed, with promising results to effectively and efficiently integrate renewable resources into the electric power grid on a large scale.

This thesis presents a novel, fast, and accurate 3 steady-state power-flow analysis (PFA) tool for the real-time operation of the active distribution systems, also known as the active distribution networks (ADN), in the grid-tied and islanded operating modes. Three-phase power-flow models of loads, transformers, and multi-phase power lines and laterals are provided. This thesis also presents novel steady-state, fundamental-frequency, power-flow models of voltage-sourced converter (VSC)-based distributed energy resource (DER) units. The proposed models address a wide array of DER units, i.e., (i) variable-speed wind-driven doubly-fed asynchronous generator-based and (ii) single/three-phase VSC-coupled DER units. In addition, a computationally-efficient technique is proposed and implemented to impose the operating constraints of the VSC and the host DER unit within the context of the developed PFA tool. Novel closed forms for updating the corresponding VSC power and voltage reference set-points are proposed to guarantee that the power-flow solution fully complies with the VSC constraints. All the proposed DER models represent (i) the salient VSC control strategies and objectives under balanced and unbalanced power-flow scenarios and (ii) all the operating limits and constraints of the VSC and its host DER unit. Also, the slack bus concept is revisited, associated with the PFA, where a 3 distributed slack bus (DSB) model is proposed for the PFA and operation of islanded ADNs. Distributing the real and reactive slack power among several DER units is essential to provide a realistic power-flow approach for ADNs in the absence of the utility bus. The proposed DSB model is integrated with the developed 3 PFA tool to form a complete ADN PFA package. The new PFA tool, including the proposed DER and DSB models, is tested using several benchmark networks of different sizes, topologies, and parameters. Many case studies, encompassing a wide spectrum of DER control specifications and operating modes, are conducted to demonstrate (i) the numerical accuracy of the proposed models of the DER units and their operating constraints, (ii) the effectiveness of the proposed DSB model for the islanded ADN PFA, and (iii) the computational efficiency of the integrated PFA software tool irrespective of the network topology and parameters.

This thesis presents a novel, fast, and accurate 3 steady-state power-flow analysis (PFA) tool for the real-time operation of the active distribution systems, also known as the active distribution networks (ADN), in the grid-tied and islanded operating modes. Three-phase power-flow models of loads, transformers, and multi-phase power lines and laterals are provided. This thesis also presents novel steady-state, fundamental-frequency, power-flow models of voltage-sourced converter (VSC)-based distributed energy resource (DER) units. The proposed models address a wide array of DER units, i.e., (i) variable-speed wind-driven doubly-fed asynchronous generator-based and (ii) single/three-phase VSC-coupled DER units. In addition, a computationally-efficient technique is proposed and implemented to impose the operating constraints of the VSC and the host DER unit within the context of the developed PFA tool. Novel closed forms for updating the corresponding VSC power and voltage reference set-points are proposed to guarantee that the power-flow solution fully complies with the VSC constraints. All the proposed DER models represent (i) the salient VSC control strategies and objectives under balanced and unbalanced power-flow scenarios and (ii) all the operating limits and constraints of the VSC and its host DER unit. Also, the slack bus concept is revisited, associated with the PFA, where a 3 distributed slack bus (DSB) model is proposed for the PFA and operation of islanded ADNs. Distributing the real and reactive slack power among several DER units is essential to provide a realistic power-flow approach for ADNs in the absence of the utility bus. The proposed DSB model is integrated with the developed 3 PFA tool to form a complete ADN PFA package. The new PFA tool, including the proposed DER and DSB models, is tested using several benchmark networks of different sizes, topologies, and parameters. Many case studies, encompassing a wide spectrum of DER control specifications and operating modes, are conducted to demonstrate (i) the numerical accuracy of the proposed models of the DER units and their operating constraints, (ii) the effectiveness of the proposed DSB model for the islanded ADN PFA, and (iii) the computational efficiency of the integrated PFA software tool irrespective of the network topology and parameters.

This thesis presents a novel approach for a power system to find a practical power flow solution when all the generators in the system have hit their real power output limits, such as some generator units shutting down or load outages. The approach assumes the frequency of the system is unable to be kept at the rated value (usually 60 or 50 Hz) and accordingly, the generator real power outputs are affected by the system frequency deviation. The modification aims to include the system frequency deviation as a new state variable in the power flow so that the power system can be described in a more precise way when the generation limits are hit and the whole system is not operated under the normal condition. A new mathematical formulation for power flow is given by modified the conventional power flow mismatch equation and Jacobian matrix. The Newton – Raphson method is particularly chose to be modified because Newton – Raphson method is most widely used and it is a fast convergent and accurate method. The Jacobian matrix will be augmented by adding a column and a row. Matlab is used as a programming tool to implement the Power Flow for Long Term Frequency Stability (PFLTFS) method for a simple 4-bus system and the IEEE 118-bus system. And PSS/E Dynamic simulation is used to verify the steady state solution from PFLTFS is reasonable. The PSS/E Dynamic Simulation plots are used to analyze the long term frequency response. The PFLTFS method provides a technique for solving an abnormal state system power flow. From the results we can conclude that the PFLTFS method is reasonable for solving power flow of a real power unbalanced system.

Κύριος στόχος αυτής της εργασίας είναι η παρουσίαση ενός μοντέλου ανάλυσης ροής φορτίου (ΑΡΦ) το οποίο να ανταποκρίνεται στα σύγχρονα συστήματα διανομής με κατανεμημένη παραγωγή. Η ανάλυση ροής φορτίου είναι μία από τις βασικότερες τεχνικές που χρησιμοποιούνται στην μόνιμη ημιτονοειδή κατάσταση ενός συστήματος ηλεκτρικής ενέργειας και ορίζει την βέλτιστη λειτουργία του. Με την ευρεία εισαγωγή στα ΣΗΕ των ανανεώσιμων πηγών, η δομή των παραδοσιακών ΣΗΕ έχει αλλάξει. Σημαντικό μέρος της κατανάλωσης τροφοδοτείται τοπικά και κοντά στα φορτία. Η παραγωγή επομένως αποκτά ολοένα και περισσότερα χαρακτηριστικά κατανεμημένης παραγωγής. Η κατανεμημένη παραγωγή αναπτύσσεται ραγδαία τα τελευταία χρόνια στα συστήματα διανομής. Εξαιτίας αυτής της ανάπτυξης και αλλαγής της δομής του συστήματος επηρεάζεται και η ανάλυση ροής φορτίου. Στην παραδοσιακή ανάλυση ροής φορτίου δεν υπάρχουν πληροφορίες για την κατανομή φορτίου και των απωλειών μεταξύ των κατανεμημένων παραγωγών και της παραγωγής από το σύστημα ηλεκτρικής ενέργειας.. Για τον λόγο αυτό νέα μοντέλα ανάλυσης ροής φορτίου θα πρέπει να σχεδιαστούν. Με την παρούσα εργασία γίνεται μία προσπάθεια επανατοποθέτησης και νέας επίλυσης του προβλήματος της ανάλυσης ροής φορτίου ώστε αυτή να λαμβάνει υπόψη τις κατανεμημένες παραγωγές και την παραγωγή του ΣΗΕ, υπό την έννοια ότι και η κατανεμημένη παραγωγή ορίζεται σε κάθε βήμα και δεν θεωρείται εξαρχής σταθερή. Για το σκοπό αυτό επιλέγει μία νέα κατάστρωση του προβλήματος η οποία η οποία αντικαθιστά τον ζυγό αναφοράς με ένα μοντέλο κατανεμημένου ζυγού αναφοράς στις γεννήτριες παραγωγής του κατανεμημένου συστήματος. Το μοντέλο κατανεμημένου ζυγού αναφοράς εισαγάγει παράγοντες συμμετοχής για την κάθε επιμέρους παραγωγή, οι οποίοι είναι ανάλογοι της επίδρασης που έχει η κάθε μία στις απώλειες του συστήματος. Στην συνέχεια οι παράγοντες συμμετοχής υπολογίζονται με την έννοια των περιοχών γεννήτριας. Η περιοχή μίας γεννήτριας ορίζεται με βάση τη φορά ενεργού ισχύος. Αφού αυτή οριστεί, βρίσκεται η συνεισφορά κάθε παραγωγής στις απώλειες του συστήματος. Είναι προφανές ότι η περιοχή τοποθέτησης των παραγωγών καθώς και οι παράμετροι δικτύου επηρεάζουν την κατανομή των απωλειών σε αυτές. Έτσι δοκιμάζεται μία νέα μέθοδος ΑΡΦ με την τεχνική Newton-Raphson βασισμένη στη νέα δομή του συστήματος. Τα αποτελέσματα δείχνουν να είναι ενθαρρυντικά και βελτιστοποιούν τη συμμετοχή της κατανεμημένης παραγωγής στο σύστημα. / Distribution system operating environments are changing rapidly. With large number of distributed generators (DGs) installed within distribution systems, distribution systems are facing great challenges: the traditional methods for distribution system analysis and planning needs to be revised, and new tools have been developed. This thesis addresses these challenges by using a method of slack bus new modeling. The concept of the distributed slack bus model is used for distribution system analysis and planning. Its impacts on distribution applications are also investigated. The method introduces scalar participation factors to distribute uncertain real power system loss for three-phase power flow calculations. It provides a method to calculate network-based participation factors by using the generator domain based method. Three-phase power flow is a vital analysis tool for distribution systems. In this work, the main objective is to study slack bus modeling and to use the new distributed slack bus model for three-phase power flow. The new method of power flow analysis is tested in a simple power system and the results are satisfactory.

As novas tecnologias FACTS aplicadas ao sistema de transmissão, com base em eletrônica de potência, podem também ser úteis à distribuição. Para tal é preciso conduzir um procedimento de consolidação da utilização e do desempenho destas, para sua aplicação sem riscos. Neste trabalho, dois aspectos serão contemplados. O primeiro se refere à aplicação do dispositivo FACTS atuando como um capacitor série. Em se tendo controle de módulo e da fase da tensão inserida em série com a linha pode-se fazê-la comportar-se como uma queda em uma reatância série capacitiva ou indutiva. O controle dessa reatância série (aumentando/diminuindo) permitirá a aplicação do conceito de compensação série em qualquer ponto do sistema de distribuição, provendo benefícios de um controle contínuo da tensão e também do controle do fluxo de carga no sistema independente da corrente. O segundo aspecto refere-se ao uso dos dispositivos na conexão de alimentadores controlando a potência ativa entre eles. Para esta operação outro dispositivo UPFC, com conceito similar ao descrito acima, entretanto atuando na fase da tensão entre 2 barras, comporta-se como um transformador defasador com variação contínua de ?taps?, podendo controlar a potência ativa entre os alimentadores. A aplicação destas tecnologias propiciarão vários benefícios para a expansão da distribuição tais como, flexibilização do uso da rede, interligação de alimentadores permitindo manobras de blocos de energia sem ?pisca?, ajuste contínuo do suporte de reativos durante a operação, controle dinâmico do fluxo de potência. O objetivo deste trabalho é estudar a aplicabilidade da tecnologia FACTS e estender este conceito para aplicação em sistemas de distribuição e conduzir simulações digitais em redes de distribuição (15kV) identificando o desempenho e os benefícios atingidos. O programa de simulação utilizado é o ATP (Alternative Transients Program). / The new FACTS technologies applied to the transmission system, based on power electronics, can also be useful to the distribution. For that, it is necessary to drive a procedure to consolidate the use and the performance for their application without risks. In this work two aspects will be approached. The first refers to the application of a FACTS device acting as series compensator. This device will be able to control the voltage in module and phase in order to act as a voltage drop in a serie reactance with capacitive or inductive features. The control of this series reactance (increasing/ decreasing) will allow the application of series compensation concept to any point of the distribution system, providing the benefits of continuous control of the voltage added to the load flow control in the system independent of the current. The second aspect refers to its use in the connection of two feeders controlling the active power between them. For this operation other device, UPFC, with similar concept as described previously, acts mainly in the phase of the injected voltage in the line, performing as a phase-shift with continuous taps variation and is able to control the active power flow between feeders. The application of this technology will provide several benefits for the distribution expansion, such as, a greater flexibility in the use of the network, connection of feeders without load flow interruption, continuous adjust of reactive power during the operation and dynamic control of power flow. The purpose of this work is to study the applicability of the FACTS technology, to extend this concept for the application in the distribution system by using digital simulations in distribution network up to 15kV identifying the performance and the reached benefits.

Made available in DSpace on 2014-06-11T19:30:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-07-21Bitstream added on 2014-06-13T19:00:51Z : No. of bitstreams: 1 amorim_ea_dr_ilha.pdf: 1200042 bytes, checksum: 598a8d060889d642964ac8c022c167e1 (MD5) / Esta pesquisa tem por objetivo o desenvolvimento de uma ferramenta computacional para a solução do problema de Fluxo de Potência Ótimo Multimercado (FPOM). O problema de fluxo de potência ótimo mutimercado é decomposto em vários subproblemas, uma para cada, submercado que compõe o sistema de potência interconectado. O modelo de decomposição utilizado permite resolver o problema de FPO considerando-se os modelos de mercado desverticalizados e centralizados e os desverticalizados e descentralizados. Neste contexto, a pesquisa desenvolvida considera o novo esquema de funcionamento dos mercados de energia elétrica, no qual é vi freqüentemente desejável preservar a autonomia de cada um dos submercados que compõem o sistema de potência multimercado. O problema de FPO proposto é modelado como um problema de otimização não-linear inteiro misto, com variáveis de controle contínuas e discretas e têm ênfase no despacho econômico da geração de potência ativa e nos ajustes dos controles de tensão. Além disso, este modelo de FPO trata os subproblemas ativo e reativo simultaneamente. Para a sua solução é apresentado um algoritmo evolutivo multiobjetivo, baseado no NSGA (Nondominated Sorting Genetic Algorithm), pois características do problema abordado dificultam a sua solução através das técnicas baseadas em programação matemática e justificam a escolha da metaheurística multiobjetivo. / This research is aimed at developing a computational tool for the solution of the Multimarket Optimal Power Flow (MOPF) problem. The multimarket optimal power flow problem is decomposed in various subproblems, one for each submarket that is part of the interconnected power system. The decomposition model used here allows solving the OPF problem considering the deregulated and centralized, and the deregulated and decentralized market models. In this context, the developed research takes into account the new functioning scheme of the electric power markets, viii where it is frequently desirable to preserve the autonomy of each one of those submarkets that compose the multimarket power system. The proposed OPF problem is modeled as a mixed integer non-linear optimization problem with continuous and discrete control variables, emphasizing the economic dispatch of the active power generation and the voltage control adjustments. In addition, this model of OPF deals simultaneously with the active and reactive subproblems. For its solution, a multiobjective evolutionary algorithm based on the NSGA (Nondominated Sorting Genetic Algorithm) is presented. The characteristics of the problem make difficult the utilization of techniques based on mathematical programming, justifying the adoption of a multiobjective metaheuristic.