Σκοπός της παρούσας διπλωματικής εργασίας είναι η παρουσίαση των κυριότερων μεθόδων παραγωγής ηλεκτρικής ενέργειας και η ανάλυση όλων των οικονομικών παραμέτρων ώστε να επιτύχουμε τη σχεδίαση του βέλτιστου συστήματος. Στο πρώτο κεφάλαιο γίνεται μία παρουσίαση των κυριότερων μονάδων παραγωγής ενέργειας. Αναφέρονται οι αρχές λειτουργίας και το κύκλωμα πάνω στην οποία βασίζεται ο κάθε σταθμός, ο βαθμός απόδοσης του κάθε συστήματος και τα πλεονεκτήματα και μειονεκτήματα αυτών. Αρχικά παρουσιάζονται οι ατμοηλεκτρικές, οι αεριοστροβιλικές και οι συνδυασμένου κύκλου συμβατικές μονάδες. Εξηγείται ο θερμοδυναμικός κύκλος λειτουργίας του Rankine πάνω στον οποίο βασίζεται η λειτουργία τους και οι προϋποθέσεις βέλτιστης λειτουργίας. Περιγράφεται ο κύκλος λειτουργίας και οι μετατροπές ενέργειας που πραγματοποιούνται στους στροβίλους και τα πρόσθετα μηχανήματα. Στην συνέχεια γίνεται αναφορά στους υδροηλεκτρικούς σταθμούς ροής ποταμού και αποθήκευσης ενέργειας. Εξηγείται η μελέτη για την δημιουργία ενός τέτοιου σταθμού, αναλύονται οι υποδομές και οι κτιριακές εγκαταστάσεις που απαιτούνται. Κατόπιν, περιγράφονται οι πυρηνικοί σταθμοί. Αναλύεται η πυρηνική σχάση, παρουσιάζεται ο πυρηνικός αντιδραστήρας και τα είδη του. Εν συνέχεια, επισημαίνονται οι ανανεώσιμες πηγές ενέργειας. Για τα αιολικά συστήματα μελετάται η εγκατάστασή τους και τα κύρια χαρακτηριστικά τους. Αναφέρεται η δομή της ανεμογεννήτριας, η αρχή λειτουργίας και τα διάφορα είδη ανεμογεννητριών και αιολικών πάρκων που βρίσκουν εφαρμογή σήμερα. Για τα φωτοβολταϊκά συστήματα, περιγράφεται η βασική αρχή λειτουργίας τους, το φωτοβολταϊκό φαινόμενο καθώς και η δομή του συστήματος. Αναλύονται τα συστήματα επίπεδων και συγκεντρωτικών πλαισίων που υπάρχουν και οι διάφορες συσκευές που απαρτίζουν το φωτοβολταϊκό σύστημα. Επίσης, περιγράφονται τα συστήματα που είναι συνδεδεμένα στο δίκτυο, καθώς και τα απομονωμένα. Κλείνοντας το κεφάλαιο, αναφέρονται τα γεωθερμικά συστήματα, οι κυψέλες καυσίμου και τα συστήματα παραγωγής ηλεκτρισμού από ενέργεια βιομάζας και παλιρροϊκής. Στο δεύτερο κεφάλαιο παρουσιάζονται οι πηγές ενέργειας και συγκεκριμένα τα ορυκτά καύσιμα. Γίνεται μία κατηγοριοποίηση σύμφωνα με τον ενεργειακό πόρο, εξετάζοντας τα αποθέματα, τη ζήτηση και την παραγωγή τους. Δίνονται πληροφορίες για το πετρέλαιο, το φυσικό αέριο, τον άνθρακα και τα πυρηνικά καύσιμα. Ιδιαίτερη έμφαση δίνεται στον λιγνίτη, λόγω των αποθεμάτων που υπάρχουν στην χώρα μας, και παρατίθεται μία ανάλυση ενός λιγνιτικού θερμοηλεκτρικού συστήματος. Στο τρίτο κεφάλαιο παρουσιάζεται ο τρόπος σχεδιασμού ενός βέλτιστου συστήματος. Για την παραγωγή του βέλτιστου συστήματος πρέπει να ληφθούν υπόψη πολλοί παράμετροι που περιλαμβάνουν την πηγή ενέργειας, τον τύπου του ενεργειακού συστήματος, την εκτίμηση του κόστους παραγωγής και των εγκαταστάσεων καθώς και την επιλογή τοποθεσίας. Αυτές οι αποφάσεις βασίζονται σε έναν αριθμό από τεχνικούς, οικονομικούς και περιβαλλοντικούς παράγοντες που είναι σε μεγάλο βαθμό άσχετοι μεταξύ τους. Αναφέρονται οι μέθοδοι υπολογισμού του κόστους συντήρησης και λειτουργίας ενός ενεργειακού συστήματος. Γενικά ως συμπέρασμα δεν μπορούμε να καταλήξουμε σε έναν κανόνα, γιατί η βέλτιστη λύση είναι απόρροια αναγκών, προτεραιοτήτων και παραμέτρων που προκύπτουν σε κάθε περίπτωση Στο τέταρτο κεφάλαιο αναπτύσσεται μία μελέτη οικονομικής φύσεως. Για μια ενεργειακή επένδυση είναι απαραίτητη μία ανάλυση δαπανών του κύκλου ζωής της. Μέσω της ανάλυσης αυτής αξιολογούνται οι συνολικές κύριες και λειτουργικές δαπάνες, λαμβάνεται υπόψη η «χρονική αξία» των χρημάτων και ενσωματώνονται οι διακυμάνσεις στην τιμή των καυσίμων. Η ανάλυση δαπανών κύκλων ζωής εξετάζει το κόστος κατά τη διάρκεια της ζωής του συστήματος και όχι μόνο το αρχικό κόστος. Έτσι είναι ευκολότερη η συγκριτική μελέτη των συστημάτων που θέλουμε να εγκαταστήσουμε. Στο πέμπτο κεφάλαιο ως αποτέλεσμα ενός οικονομικότερου οπότε και βέλτιστου συστήματος αναφέρεται η συμπαραγωγή ηλεκτρισμού και θερμότητας. Τα συστήματα Συμπαραγωγής Ηλεκτρισμού και Θερμότητας παράγουν ταυτόχρονα αξιοποιήσιμη ηλεκτρική και θερμική ενέργεια μέσω ενός ενιαίου συστήματος. Η παραγόμενη θερμότητα μπορεί να χρησιμοποιηθεί τόσο για θερμική χρήση όσο και για ψύξη ή κλιματισμό. Βασικό πλεονέκτημα και κίνητρο εφαρμογής της αποτελεί η αυξημένη απόδοση του συστήματος, έναντι της χωριστής λειτουργίας συμβατικών συστημάτων ηλεκτροπαραγωγής και θερμικής ενέργειας. Η εξοικονόμηση αυτή προκύπτει από την ανάκτηση και αξιοποίηση της θερμότητας, που διαφορετικά θα απορριπτόταν στο περιβάλλον Στο έκτο και τελευταίο κεφάλαιο παρουσιάζεται το ελληνικό σύστημα παραγωγής ηλεκτρικής ενέργειας. Το Ελληνικό ενεργειακό σύστημα βρίσκεται την τελευταία δεκαετία σε φάση σημαντικών αλλαγών. Η διείσδυση του φυσικού αερίου, η κατασκευή των διευρωπαϊκών δικτύων, η προώθηση των ανανεώσιμων πηγών ενέργειας και εξοικονόμησης ενέργειας και τέλος η απελευθέρωση της αγοράς ηλεκτρικής ενέργειας αποτελούν τα νέα δεδομένα του. Σημαντικές είναι οι επιπτώσεις των νέων αυτών δεδομένων στην ασφάλεια του ενεργειακού εφοδιασμού της χώρας, στην μείωση της εξάρτησης της από το εισαγόμενο πετρέλαιο, με όλα τα συνεπαγόμενα οφέλη στην εθνική οικονομία, στην εξοικονόμηση μη ανανεωνόμενων ενεργειακών πόρων, στην αύξηση της αποδοτικότητας των διαδικασιών παραγωγής και κατανάλωσης ενέργειας, στην προστασία του περιβάλλοντος και τέλος στην βελτίωση των παρεχομένων υπηρεσιών στους καταναλωτές. / The subject of this diploma thesis is the study of the types of electric generation systems and their comparative study. Initially are presented summarizing the basic principles of operation and the particular characteristics of each station. The energy systems being analyzed are steam cycle, gas fired, combined cycle, hydroelectric, nuclear power, solar, wind, geothermal and biomass systems. A brief description of fuels takes place presenting oil, natural gas, coal and its derivatives and nuclear fuels. Accent is given in the lignite and a short description of a lignite thermoelectric station is given. Then, the criteria are mentioned which are suitable for the choice of optimal energy system such as operational and functional costs, prices of fuels, types of generation system and technical and environmental issues. Also an economic study is realized. A life cycle cost analysis that evaluates the total owning and operating cost and takes into account the “time value” of money. Furthermore, the co-production of energy and heat as emanation of the most optimal system is included. Finally, the energy situation that prevails in Greece is presented.

A utilização de conversores multiníveis tem sido uma importante alternativa para aplicações de alta potência e média tensão, graças aos altos níveis de potência alcançáveis por estas estruturas. Recentemente, esta topologia de conversores foi aplicada em sistemas com fontes alternativas para alimentar um sistema de geração distribuída, nos quais diferentes fontes de energia eram utilizadas. Com base nas características dos conversores multinível e sua potencial aplicabilidade em sistemas de geração distribuída, este trabalho tem como objetivo construir um sistema multinível conectado a rede de distribuição para utilização de fontes alternativas de energia como fontes primárias. Considerando que a energia fornecida pelas fontes alternativas pode sofrer variações, propõe-se a integração de sistemas armazenadores de energia, como capacitores, ao sistema multinível. Por isso, este trabalho desenvolve uma estratégia de controle para máxima transferência de potência ativa entregue à rede a fim de obter um fluxo ótimo. A topologia multinível deste trabalho possui em sua configuração dois módulos inversores conectados em série. Neste caso, é possível que pelo menos um desses inversores funcione com uma modulação em baixa frequência processando a maior parcela de potência. Assim, duas estratégias de controle modulação de fase e modulação de amplitude para a transferência de potência realizada pelo inversor de baixa frequência são analisadas. As vantagens e desvantagens de cada um dos métodos são expostas e então a estratégia mais adequada, no caso a modulação de amplitude, é utilizada na operação do conversor multinível. Além disso, são apresentados a modelagem das plantas e o projeto dos controladores de cada um dos módulos inversores. Por fim, a validação da proposta é feita através dos resultados de simulações e experimentais que mostram a capacidade do sistema de geração em transferir potência constante para a rede de distribuição e manter a corrente quase sem distorções em fase com a tensão. / The utilization of multilevel converters has been an important alternative for medium voltage applications with high power and power quality demand, thanks to the high power levels achievable for this kind of structure. Recently, this converter topology was proposed as a new possibility in renewable energy source applications, mainly in system delivering power to the grid, where different renewable energy resources may be used. Based on the characteristics of multilevel converters, and their potential applicability in distributed generation systems, this study aims to build a multilevel system that could be powered by renewable energy sources as primary sources and then connect them to a distribution grid. However, considering the energy produced by alternative sources can vary, it is analyzed the integration of a storage energy system in this multilevel topology. Taking into account this ends, the main concern of this study is related to the development of a control strategy to maximize the active power transferred to the grid. The multilevel topology employed in this study has two H-bridge inverter modules connected in series forming a cascaded configuration. Therefore, it is possible that at least one of these inverters, operating with a low frequency of modulation, process the majority of power with lower amount of losses. On this way, two control strategies for power transfer are analyzed. The advantages and disadvantages of each method are presented, and the most appropriated strategy is used in the operation of the multilevel converter system. In addition, it has been presented the design criteria for each controller and finally the validation of the proposed approach is done by mains of simulations and experimental results which show the ability of the converter to transfer constant active power to the grid and keep the grid current in phase with the grid voltage.

Concerns about climate change brought about by the increasing usage of fossil fuels has made it imperative to develop sustainable energy usage based on renewable sources. Micro-hydel plants are an important source of renewable energy that can be exploited to supply requirements of local loads in remote locations while operating as an isolated source, or the larger network when operating in grid connected mode. The focus of this research is to develop an alternative topology to the one currently in use in micro-hydel power plants. While existing plants are based on a ballast-controlled, fixed-speed, operator-supervised model, the proposed work introduces a ballast-free, variable-speed generator capable of unsupervised operation. Conventional micro-hydel generators use o-the-shelf machines with the purported aim of reducing costs. They run at a fixed speed, maintaining constant electrical load by switch-ing a plant-situated ballast load to compensate for consumer load changes. Although the intention is to have a simplified control scheme and reduced costs, the conventional plants end up being expensive since the balance-of-system costs are increased. The plant re-quires supervision by a trained operator and frequent maintenance, failing which the reliability suers. The cost and maintenance reduction possible is analysed by comparing the proposed topology with a typical well designed conventional micro-hydel plant. The proposed topology takes the characteristics of the turbine into account, and by running at variable speed, ensures that only as much power is generated as required by the consumer load. This eliminates the ballast load and associated problems present in conventional plants. The generator can be connected to the grid, if present, enabling the available power to be fully utilized. The behavior of a hydraulic turbine operating at a fixed head and discharge rate with no flow control is analyzed. Based on the turbine characteristics, a generator topology is developed, which operates in a speed range dictated by the characteristics of the turbine. Continual supervision is unnecessary since the operation of the generator is within safe limits at all times. A simple emulator that can mimic the steady state and dynamic behaviour of the turbine is developed to test the proposed generator. The two-machine wound rotor generator proposed has an auxiliary exciter similar to a conventional brushless alternator with the additional provision for bidirectional power transfer. The shaft mounted rotor side electronics facilitate brushless operation, and to-gether with the stator side controllers form an embedded system that does away with having to tune the plant in-situ. The control scheme is evaluated for expected perfor-mance in dierent operating modes. The thesis also discusses an optimization of the synchronous speed of the generator with respect to the turbine characteristics. This minimizes the bidirectional slip power transfer requirements of the rotor side converters and leads to the lowest rating for the auxiliary machine. The proposed generator can then operate like a conventional synchronous gen-erator in the grid connected mode with a simplified control scheme.

No description available.

Continued increase in system load leading to a reduction in operating margins, as well as the tendency to move towards a deregulated grid with renewable energy sources has increased the vulnerability of the grid to blackouts. Advanced intelligent techniques are therefore required to design new monitoring schemes that enable smart grid operation in a secure and robust manner. As the grid is highly interconnected, monitoring of transmission and distribution systems is increasingly relying on digital communication. Conventional security assessment techniques are slow, hampering real-time decision making. Hence, there is a need to develop fast and accurate security monitoring techniques. Intelligent techniques that are capable of processing large amounts of captured data are finding increasing scope as essential enablers for the smart grid. The research work presented in this thesis has evolved from the need for enhanced monitoring in transmission and distribution grids. The potential of intelligent techniques for enhanced system monitoring has been demonstrated for disturbed scenarios in an integrated power system. In transmission grids, one of the challenging problems is network partitioning, also known as network area-decomposition. In this thesis, an approach based on relative electrical distance (RED) has been devised to construct zonal dynamic equivalents such that the dynamic characteristics of the original system are retained in the equivalent system within the desired accuracy. Identification of coherent generators is another key aspect in power system dynamics. In this thesis, a support vector clustering-based coherency identification technique is proposed for large interconnected multi-machine power systems. The clustering technique is based on coherency measure which is formulated using the generator rotor measurements. These rotor measurements can be obtained with the help of Phasor Measurement Units (PMUs). In distribution grids, accurate and fast fault identification of faults is a key challenge. Hence, an automated fault diagnosis technique based on multi class support vector machines (SVMs) has been developed in this thesis. The proposed fault location scheme is capable of accurately identify the fault type, location of faulted line section and the fault impedance in the distributed generation (DG) systems. The proposed approach is based on the three phase voltage and current measurements available at all the sources i.e. substation and at the connection points of DGs. An approach for voltage instability monitoring in 3-phase distribution systems has also been proposed in this thesis. The conventional single phase L-index measure has been extended to a 3-phase system to incorporate information pertaining to unbalance in the distribution system. All the approaches proposed in this thesis have been validated using standard IEEE test systems and also on practical Indian systems.

Over the last decade, power systems have evolved dramatically around the world, owing to higher demand, stringent requirements on quality and environmental concerns that are becoming increasingly critical. With the introduction of new technologies like large-scale renewable energy, wide-area measurement based on phasor measurement units (PMUs) and consumer interaction in the distribution system, the power grid today has become more potent than ever before. Most of the defining features of the smart grid today rest on the integration of advanced communication capabilities into the grid. While communication infrastructure has become a key enabler for the smart grid, it also introduces new and complex control challenges that must be addressed. As we increasingly rely on information transmitted to distant areas over communication networks, it becomes imperative to model the effects of the communication system on the stability of the power grid. Several approaches exist in control theory to study such systems, widely referred to as Networked Control Systems (NCS). Networked control theory provides mathematical tools for system stability analysis and control in the presence of communication delays, packet dropouts and disordering due to transmission of sensor and actuator signals via a limited communication network. In this thesis, a networked control framework for smart grids with integrated commu-nication infrastructure (ICT) is developed. In particular, a networked control systems perspective is developed for two scenarios - wide-area monitoring control, and coordinated control of distributed generation sources. The effects of communication delays and packet dropouts on power system stability are modeled in detail. In the wide-area monitoring control problem, system state measurements are trans-mitted from remote locations through a communication network. The system is modeled as an NCS and a control design approach is presented to damp inter-area oscillations arising from various power system disturbances in the presence of communication constraints. In the coordinated control scenario, a power system with geographically dispersed sources is modeled as an NCS. A networked controller is designed to stabilize the system in the presence of small signal disturbances when system measurements are subject to communication delays and packet dropouts. A realistic output feedback networked control scheme that only uses voltage measurements from PMUs is also developed for practical implementation. The networked controllers designed in this thesis are validated against controllers designed by standard methods, by simulation on standard test systems. The networked controllers are found to enhance power system stability and load transfer capability even in the presence of severe packet dropouts and delays. Several extensions and theoretical problems motivated by this thesis are also proposed.