Durant la dernière décennie, de nouveaux concepts ont émergé dans le domaine de l'électricité, notamment les Smart Grids, la génération distribuée et les Microgrids (MGs). Dans cette thèse, nous nous concentrons principalement sur l'étude des MGs. Selon les prévisions des spécialistes du domaine, les MGs devraient prendre une place de plus en plus importante dans les futurs systèmes électriques. Mais pour cela, ils devront être mieux gérés, et il faudra donc d’abord résoudre plusieurs problèmes importants : l’identification, la mobilité, l’aspect multi-rôles, l’interopérabilité, la non-coopération et la planification de l’offre et la demande de l’électricité. Afin de résoudre tous ces problèmes, nous proposons un Framework dédié composé de 3 couches : physique, de connaissance et de gestion. Trois principales contributions sont présentées dans ce travail ciblant la résolution des problèmes déjà cités : OntoMG : un modèle d'information ontologique pour les Microgrids, DECF : un modèle coopératif pour l’optimisation de l’échange d’électricité dans le MG, et MOCSF : une planification coopérative multi-objectifs de l’électricité dans le MG. OntoMG est un modèle ontologique de données, basé sur les standards IEC 61970 et IEC 61580, complété par un nombre de paramètres additionnels permettant au MG d’atteindre l’ensemble de ses objectifs. Notre approche présente plusieurs avantages par rapport aux approches existantes dans la littérature scientifique, notamment : elle permet une planification de la consommation, la production et le stockage de l’électricité dans le MG, elle considère plusieurs sources d'énergie contrairement aux approches existantes qui ne prennent en compte que l'interaction des consommateurs avec une seule source d'énergie, et elle prend en compte l’ensemble des préférences des composants du MG à la différence des approches existantes qui ne considèrent ces préférences qu’en partie. / Over the past decade, new concepts have emerged in the electricity field, including the Smart Grids, the Distributed Generation and the Micro- grids (MGs). In this thesis, we will be mainly focusing on the study of the MGs. An MG is a small-scale power system, consisting of local power generation, local loads and energy storage systems. Thanks to their numerous economical, ecological and operational benefits, the MGs are expected to hold the promise of becoming a major ingredient in the implementation of the future power systems. However, there are several significant challenges to overcome in order to achieve its expected bene- fits, namely: the cyber-attacks, the mobility aspect, the interoperability, the non-cooperation, and the demand-side management. Three main contributions are developed. First, we present OntoMG, an ontology-based data model, capable of representing the heterogeneous components of the MG and their properties, while being compliant with existing models and information standards (i.e., IEC 61970 and IEC 61850) and coping with the interoperability issues and the multi-objective aspect of MG. Secondly, we introduce DECF, a cooperative model for the optimization of the electricity exchange in the MG, offering several advantages over existing approaches, in particular: 1) its generic in that it considers all heterogeneous components of MG, 2) it is a cooperative model that reduces the technical, ecological and economic costs and encourages the local power exchange, and 3) it is user-oriented in that it gives the user the possibility to fine-tune the weight of each objective aspect . Finally, we introduce MOCSF, a ‘Multi-objective Cooperative Scheduling Framework’ designed for scheduling the production, consumption and storage in the MG. MOCSF 1) provides a multi-type scheduling in that it allows the scheduling of all the power consumption, production and storage of the MG, 2) considers multiple energy sources and 3) considers the MG components’ preferences. After detailing the existing power scheduling techniques and their drawbacks regarding our challenges, we presented our ‘MOCSF’ modules: The Preference-based compromise builder, designed to generate the best balance between the sellers and buyers desired schedules and the Multi-Objective Scheduler, aiming at scheduling the seller-to-buyer associations resulting from the DECF, while reducing the operational, economic and ecological costs of the MG. An illustrative example is provided after each step to ease the understanding of each module. Finally, a set of experiments showed the performance and efficiency of our approach. Illustrative examples are provided after each step to facilitate understanding of each module. Then, a number of simulations are made to show the effectiveness of our approaches to solve our challenges in relation to the existing approaches.

Opportunities for enhancing the security and reliability of power supply as well as the utilization of renewable and efficient energy sources have generated major interest in Microgrids. A microgrid typically consists of interconnected loads, distributed generators (DG) and energy storages, and should be able to operate in parallel with the utility grid or as a power-island. The main focus of this thesis is on the transition between parallel and islanded operation of a microgrid. A literature review on existing microgrids was carried out. Based on the survey, a microgrid test system was implemented on PSCAD/EMTDC simulation program. The microgrid controls essential for the study and a load shedding scheme were designed and implemented. When the microgrid changes from parallel to islanded operation, its controls need to be changed. It was found that delays in microgrid control mode transition can impact the amount of load need to be shed to preserve the frequency stability and the power quality of the islanded microgrid. The importance of fast detection of islanding was therefore highlighted. The IEEE standard 1547.4-2011 recommends application of the existing DG synchronization criteria for microgrid synchronization. The adequacy of these criteria for synchronization of a microgrid with highly unbalanced loading was investigated. It was found that the required criteria can be met with the support of switched capacitors for voltage balancing, and a circuit breaker supervised by a synchro-check relay is sufficient to successfully reconnect an islanded microgrid back to the utility. In order to meet the requirement for fast detection of islanding of microgrids, new islanding detection technique was proposed. In the proposed scheme, Discrete Wavelet Transform was used to extract features from transient current and voltage signals, and then a Decision Tree classifier was employed to distinguish islanding events from other transients. Simulation based tests asserted that the proposed technique has a high reliability and fast response compared to most existing islanding detection methods. Also, the detection time of the proposed method was invariant with the power imbalance in the microgrid, and gave a zero non-detection-zone with any type of generator.

Opportunities for enhancing the security and reliability of power supply as well as the utilization of renewable and efficient energy sources have generated major interest in Microgrids. A microgrid typically consists of interconnected loads, distributed generators (DG) and energy storages, and should be able to operate in parallel with the utility grid or as a power-island. The main focus of this thesis is on the transition between parallel and islanded operation of a microgrid. A literature review on existing microgrids was carried out. Based on the survey, a microgrid test system was implemented on PSCAD/EMTDC simulation program. The microgrid controls essential for the study and a load shedding scheme were designed and implemented. When the microgrid changes from parallel to islanded operation, its controls need to be changed. It was found that delays in microgrid control mode transition can impact the amount of load need to be shed to preserve the frequency stability and the power quality of the islanded microgrid. The importance of fast detection of islanding was therefore highlighted. The IEEE standard 1547.4-2011 recommends application of the existing DG synchronization criteria for microgrid synchronization. The adequacy of these criteria for synchronization of a microgrid with highly unbalanced loading was investigated. It was found that the required criteria can be met with the support of switched capacitors for voltage balancing, and a circuit breaker supervised by a synchro-check relay is sufficient to successfully reconnect an islanded microgrid back to the utility. In order to meet the requirement for fast detection of islanding of microgrids, new islanding detection technique was proposed. In the proposed scheme, Discrete Wavelet Transform was used to extract features from transient current and voltage signals, and then a Decision Tree classifier was employed to distinguish islanding events from other transients. Simulation based tests asserted that the proposed technique has a high reliability and fast response compared to most existing islanding detection methods. Also, the detection time of the proposed method was invariant with the power imbalance in the microgrid, and gave a zero non-detection-zone with any type of generator.

Σκοπός της παρούσας διπλωματικής εργασίας είναι η προστασία ενός μικροδικτύου συνδεδεμένου στο δίκτυο διανομής χαμηλής τάσης από μεγάλα ρεύματα που οφείλονται σε βυθίσεις τάσης του δικτύου διανομής. Η μελέτη θα περιλαμβάνει όλα εκείνα τα στοιχεία που είναι απαραίτητα για τη σύνδεση σε ένα δίκτυο. Συγκεκριμένα, θα περιλαμβάνει τον ανυψωτή τάσης (boost converter) ο οποίος είναι υπεύθυνος για την ανύψωση της συνεχούς τάσης εξόδου της διεσπαρμένης παραγωγής, τον αντιστροφέα (inverter) ο οποίος θα μετατρέπει την συνεχή τάση εξόδου του ανυψωτή σε εναλλασσόμενη με το επιθυμητό πλάτος κ συχνότητα, και τέλος θα περιλαμβάνει το σύστημα ελέγχου το οποίο θα προσπαθεί να ικανοποιεί τις ενεργειακές ανάγκες κάθε φορτίου ρυθμίζοντας κατάλληλα τις παραμέτρους των προηγούμενων μερών. Επιπλέον σε περιπτώσεις βύθισης τάσης η διπλωματική εργασία προτείνει μία μέθοδο ελέγχου η οποία προσπαθεί να άρει την διανυσματική πτώση τάσης στην γραμμή διασύνδεσης μικροδικτύου και δικτύου διανομής. Επειδή η μελέτη ενός τέτοιου πραγματικού συστήματος δεν ήταν εφικτή στα πλαίσια μας διπλωματικής εργασίας, επιλέχθηκε η μέθοδος εξομοίωσης σε ηλεκτρονικό υπολογιστή. Για την εξομοίωση χρησιμοποιήθηκε το πρόγραμμα PSCAD,ένα από τα πλέον καταλληλότερα προγράμματα για την μελέτη των συστημάτων ηλεκτρικής ενέργειας. Η επιλογή του PDCAD στηρίχθηκε στο γεγονός ότι είναι εξαιρετικά εύχρηστο ενώ ταυτόχρονα έχει γρήγορες αποκρίσεις και χρησιμοποιείται κατά κόρον για την προσομοίωση τέτοιων συστημάτων. / The purpose of this diplomathesis is to protect a microgrid, which is connected to low voltage distribution network, of large currents due to voltage sags in the distribution network. This study includes all the elements needed to connect the microgrid to a network. Specifically, it includes the boost converter which is responsible for raising the voltage output of dispersed production, the inverter which will convert the voltage output of the enhancer into alternating with the desired width and frequency and at last it includes the control system which tries to satisfy the energy needs of each load by adjusting appropriate parameters of the previous parameters. Moreover, in cases of voltage sags, this diploma thesis proposes a control method that attempts to eliminate the vector voltage drop in interconnection microgrid and distribution network. Since the study of such a real system was not feasible in our thesis, the method was chosen to be simulated in a computer. The simulation program that was used is the PSCAD, one of the most appropriate programs for the study of electric power systems. The choice of PSCAD relied on the fact that it is extremely handy, with fast responses and is widely used for simulating such systems.

The problem of optimum restoration after occurrence the outages in a distribution network is an important issue in smart grids. In this kind of networks remote-controlled switches, alternative sources and grid-connected distributed generators (DG) are employed. Therefore, the reliability of the system (corresponding to the frequency of failures and the duration of interruptions) is improved by operating the switches to resupply a part of interrupted system during the repair time. To evaluate the reliability indices in smart grids, neglecting the restoration during the repair time causes the wrong assessment of the network. Thus, considering the rerouting the power during the interruptions seems necessary to calculate the reliability indices. The problem of restoration is formulated as a non-linear integer programming problem with the assistance of the network graph. The circuit graph method is also used to pre-evaluate the feasible interchanging operations to enhance the efficiency of the computations. The topological and operational constraints in this formulation can be found and resolved with the assistance of fundamental cut-set matrix. The optimum restoration schemes is obtained by considering the optimal islanded mode of operation of the DGs which implies maximizing the loading of DGs while not violating their generation capacities. The optimum restoration policies lead us to find the optimum number and location of those manual switches that should be upgraded to the remote-controlled switches. This is a multi-objective problem that contains the contribution of each restoration policy in the reliability improvement and the cost of those switching operations. The proposed algorithm is applied to different standard test systems and the results are compared to the results obtained from other methods and algorithms.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2016. / Power fluctuations in a microgrid are caused by disturbances due to the connection and disconnection of Distributed Generators (DG’s), as well as the irregular input of the sun and wind renewable energy. Renewable penetration such as the sun, wind and tidal energy causes intermittency which directly affects the input and resultant output power of a microgrid. Control systems have to be implemented on three different levels to ensure the stability and reliability of the power supplied to the load. This can be achieved by implementing the following: 1) Primary control with mechanical valves and actuators to translate feedback signals through droop control. 2) Secondary control with power electronics to facilitate maximum power point tracking, phase lock loops and switch mode inverters to manipulate the electrical signals to a desired set points including PID control. 3) Tertiary control with software program management to monitor the power flow as well as to evaluate congregated logic and implement decision making. Energy storage systems like super capacitors can compensate for power imbalance by providing excess stored energy to the microgrid for short periods of time. The added advantage of capacitor banks is that it can facilitate power factor correction where inductive loads like rotating motors form large part of the total load. Battery banks can compensate for energy shortage for longer periods of time. The duration of the compensation can be determined by the size, topology and the type of batteries used. The objectives of this study is to improve the unstable power output responses of a renewable energy microgrid by designing and analysing control strategies intended at power wavering compensation which also includes energy storage. Sub control systems is created and simulated in Matlab/Simulink for analytical comparative observations. Results of the simulated model are discussed and recommendations are given for future works.

Cargas e fontes elétricas de pequeno porte, integradas através de alimentadores de distribuição de baixa tensão, agrupadas e gerenciadas de tal maneira que se comportem como uma única entidade controlável dentro de um sistema de potência e com a capacidade de operar de forma paralela ou isolada da rede elétrica convencional, constituem-se em um novo tipo de sistema elétrico conhecido como Minirrede. Esta tese aborda o problema relacionado à estabilidade dinâmica de Minirredes com controle autônomo de frequência e tensão, quando operadas de forma isolada da rede convencional. As minirredes analisadas são compostas por combinações de fontes elétricas convencionais e fontes alternativas que não geram naturalmente em 50 ou 60 Hz, sendo necessária a utilização de inversores para sua conexão com a rede elétrica. A análise se realiza no espaço de estados com metodologias baseadas nas teorias que envolvem os autovalores e autovetores da matriz de estado. Para isto, modelos no espaço de estados são desenvolvidos para cada componente da Minirrede, mantendo um compromisso entre precisão e complexidade. O caráter analítico da análise permite investigar a relação entre a estabilidade da Minirrede e os parâmetros do sistema, tais como ganhos dos controladores, dimensionamento da rede, configurações de geração, entre outros. Análises complementares de sensibilidade dos autovalores aos parâmetros elétricos do sistema permitem inferir o comportamento dinâmico de diversas configurações de Minirredes, obtendo-se importantes conclusões à respeito. Os resultados analíticos são verificados através de simulação computacional no ambiente Simulink/Matlab®. / Electrical loads and small power sources, integrated through low voltage distribution feeders, managed in such a way to behave as one controllable entity within in a power system, and with the ability to operate connected or non-connected to the conventional power system is a new kind of electrical system known as Microgrid. This thesis addresses the problem related to dynamic stability of island Microgrids with autonomous control of frequency and voltage. The Microgrids analyzed are composed of combinations of conventional and alternative power sources that do not generate electricity naturally in 50 or 60 Hz, therefore inverters are needed to provide AC network interface. The analysis is performed in the state space with methodologies based on theories involving the eigenvalues and eigenvectors of the state matrix. For this, state-space models are developed for each component of Microgrid, maintaining a compromise between accuracy and complexity. The analytical nature of this study allows investigating the relationship between the stability of Microgrid and parameters of the system, such as controller gains, network design, generation architectures, among others. Complementary sensitivity analyzes of eigenvalues to the electrical parameters of the system allow us to infer the dynamic behavior of various configurations of Microgrids, obtaining important conclusions on the matter. The analytical results are verified by computer simulation using the platform Simulink/Matlab®.

Microgrid is an essential part of the nation’s smart grid deployment plan, recognized especially for improving efficiency, reliability, flexibility, and resiliency of the electricity system. Since microgrid consists of different distributed generation units, microgrid scheduling and real-time dispatch play a crucial role in maintaining economic, reliable, and resilient operation. The control and optimization performances of the existing online approaches degrade significantly in microgrid applications with missing forecast information, large state space, and multiple probabilistic events. This dissertation focuses on these challenges and proposes efficient online learning and optimization-based approaches. For addressing the missing forecast challenges on online microgrid operations, a new fitted rolling horizon control (fitted-RHC) approach is proposed in Chapter 2. The proposed fitted-RHC approach is designed with a regression algorithm that utilizes the empirical knowledge obtain from the day-ahead forecast to make microgrid real-time decisions whenever the intra-day forecast data is unavailable. Simulation results show that the proposed fitted-RHC approach can achieve the optimal policy for the deterministic case study and perform efficiently with the uncertain environment in the stochastic case study. / Includes bibliography. / Dissertation (PhD)--Florida Atlantic University, 2021. / FAU Electronic Theses and Dissertations Collection

Orientador: André Nunes de Souza / Resumo: A crescente demanda por energia elétrica, combinada com questões ambientais e financeiras, vem promovendo a integração de unidades geradoras distribuídas nas redes de distribuição. Essa configuração topológica, construída próxima aos consumidores, consiste em um conceito chamado de microgrid, desenvolvido nos últimos anos. Esse modelo é caracterizado por um conjunto de pequenas unidades geradoras, cargas e dispositivos de armazenamento de energia, capazes de operar em modo paralelo ou isolado, em relação à rede existente. Vários estudos apontam que as microrredes influenciam o planejamento, operação e manutenção da rede de distribuição elétrica, principalmente porque as microrredes funcionam em um fluxo de energia bidirecional em vez do modo unidirecional convencional. Essa topologia de rede pode influenciar significativamente o perfil de tensão, estabilidade, qualidade de energia e comportamento de proteção do sistema elétrico. Em relação ao esquema de proteção, esses sistemas podem interferir na coordenação e seletividade dos equipamentos que constituem a rede. Nesse sentido, o objetivo desta dissertação é analisar o impacto da contribuição da corrente de curto-circuito das conexões de microrrede no sistema de proteção de sobrecorrente nas redes de distribuição convencionais. A análise é desenvolvida modelando uma rede de distribuição IEEE de 34 barras. O software OpenDss é usado em conjunto com um aplicativo Python desenvolvido para avaliar os impactos na coordenação e sel... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The growing demand for electricity, combined with environmental and financial issues, fostered the integration of distributed generating units into distribution networks. This topological configuration, build up nearby the consumers, consist of a concept called microgrid, which has been developed in recent years. This model is characterized by a set of small generating units, loads and energy store devices, capable of operating in a parallel or isolated mode, concerning the existing network. Several studies point out that the microgrids influence the planning, operation, and maintenance of the electrical distribution network, mainly because of microgrids woks with a bidirectional power flow rather than the conventional unidirectional mode. This network topology can significantly influence the voltage profile, stability, power quality, and electrical system protection behavior. Regarding the protection scheme, these systems can interfere with the coordination and selectivity of the equipment that constitutes the network. In this sense, the purpose of this dissertation is to analyze the impact of the short circuit current contribution from the micro-network connections in the overcurrent protection system in the conventional distribution networks. The analysis is developed by modeling an IEEE 34-bar distribution network. The OpenDss software is used in conjunction with a developed Python application to assess the impacts on coordination and selectivity of the overcurrent protec... (Complete abstract click electronic access below) / Mestre

Power systems have evolved significantly during the last two decades with the advent of Distributed Energy Resources (DERs) like solar PV. Traditionally, large power plants were considered as the sole source of energy in the power systems. However, DERs connected to the transmission and the distribution systems are creating a paradigm shift from a centralized generation to a distributed one. Though the variable power output from these DERs poses challenges to the reliable operation of the grid, it also presents opportunities to design control and coordination approaches to improve system efficiency and operational reliability. Moreover, building new transmission lines to meet ever-increasing load demand is not always viable. Thus, the industry is leaning towards developing non-wires alternatives. Considering the existing limitations of the transmission system, line congestions, and logistic/economic constraints associated with its capacity expansion, leveraging DERs to supply distribution system loads is attractive and thus capturing the attention of researchers and the electric power industry. The primary objective of this dissertation is to develop a framework that enables DERs to supply local area load by co-simulating the power system and transactive system representations of the network. To realize this objective, a novel distributed optimization and game theory-based network representation is developed that optimally computes the power output of the Home Microgrids/DER aggregators. Moreover, the optimum operational schedules of the DERs within these Home Microgrids/DER aggregators are also computed. The novel electrical-transactive co-simulation ensures that the solution is optimum in the context of power systems i.e. power flow constraints are not violated while the payoffs are maximized for the Home Microgrids/DER aggregators. The transactive mechanism involves two-way iterative signaling. The signaling is modeled as an infinite strategy, multiplayer, non-cooperative game, and a novel theory is developed for the game model. The dissertation also introduces a novel concept of ranking the Home Microgrids/DER aggregators according to their historic performance, thus leading to fairness, higher participation, and transparency. Significant advantages offered by the framework include consumption of local generation, transmission upgrade deferral, mitigation of line congestions in peak periods, and reduced transmission systems losses. / Doctor of Philosophy / In past, electricity was primarily produced by the large fossil fuel-based and nuclear power plants, usually located farther away from the populated areas where the bulk of the electricity consumption occurs. The electricity from the power plants is carried by the transmission lines to the populated areas where it is distributed to end-users via a distribution network. However, during the last two decades, issues like global warming and depleting fossil fuels have led to the development and increased adoption of renewable energy resources like solar photovoltaics (PV), wind turbines, etc. These resources are commonly known as Distributed Energy Resources (DERs), and they are connected to both the transmission and the distribution systems. Initially, they were mainly used to supply the load within the facility in which they are installed. However, the electric load (demand) continues to grow while adding new fossil fuel-based plants and transmission lines are becoming logistically/economically challenging. Thus, researchers are working on developing techniques that can enable DERs to supply the loads in the distribution system to which they are connected. This dissertation develops a method to use DERs for load support in the distribution systems. Specifically, the buildings that house the DERs can use the energy generated by the DERs to supply the local load (building load), and once the total generation exceeds the load demand, the building can inject the power into the distribution system to support the local area load. The proposed framework considers the electric network constraints like limits of lines supplying the power and limits of the transformers. The proposed work also develops a new method to maximize the benefit (in terms of profit) for the DER owners. A ranking system is introduced for the DER owners that enhances the transparency and fairness of the process. The key benefits offered by the proposed work include reduced losses in the transmission system, more energy consumed closer to the point of generation, and avoidance of transmission line and large central generation additions.