Traditional power plants only utilize about 30 percent of the primary energy that they consume, and the rest of the energy is usually wasted in the process of generating or transmitting electricity. On-site and near-site power generation has been considered by business, labor, and environmental groups to improve the efficiency and the reliability of power generation. Combined heat and power (CHP) systems are a promising alternative to traditional power plants because of the high efficiency and low CO2 emission achieved by recovering waste thermal energy produced during power generation. A CHP operational algorithm designed to optimize operational costs must be relatively simple to implement in practice such as to minimize the computational requirements from the hardware to be installed. This dissertation focuses on the following aspects pertaining the design of a practical CHP operational algorithm designed to minimize the operational costs: (a) real-time CHP operational strategy using a hierarchical optimization algorithm; (b) analytic solutions for cost-optimal power generation unit operation in CHP Systems; (c) modeling of reciprocating internal combustion engines for power generation and heat recovery; (d) an easy to implement, effective, and reliable hourly building load prediction algorithm.

Combined Cooling, Heating, and Power (CHP) systems have been widely recognized as a key alternative for electric and thermal energy generation because of their outstanding energy efficiency, reduced environmental emissions, and relative independence from centralized power grids. The systems provide simultaneous onsite or near-site electric and thermal energy generation in a single, integrated package. As CHP becomes increasingly popular worldwide and its total capacity increases rapidly, the research on the topics of CHP performance assessment, design, and operational strategy become increasingly important. Following this trend of research activities to improve energy efficiency, environmental emissions, and operational cost, this dissertation focuses on the following aspects: (a) performance evaluation of a CHP system using a transient simulation model; (b) development of a dynamic simulation model of a power generation unit that can be effectively used in transient simulations of CHP systems; (c) investigation of real-time operation of CHP systems based on optimization with respect to operational cost, primary energy consumption, and carbon dioxide emissions; and (d) development of optimal supervisory feedorward control that can provide realistic real-time operation of CHP systems with electric and thermal energy storages using short-term weather forecasting. The results from a transient simulation of a CHP system show that technical and economical performance can be readily evaluated using the transient model and that the design, component selection, and control of a CHP system can be improved using this model. The results from the case studies using optimal real-time operation strategies demonstrate that CHP systems with an energy dispatch algorithm have the potential to yield savings in operational cost, primary energy consumption, and carbon dioxide emissions with respect to a conventional HVAC system. Finally, the results from the case study using a supervisory feedorward control system illustrate that optimal realistic real-time operation of CHP systems with electric and thermal energy storages can be managed by this optimal control using weather forecasting information.

Combined cooling, heating and power (CCHP) systems are known as trigeneration systems, designed to provide electricity, cooling and heating simultaneously. The CCHP system has become a hot topic for its high system efficiency, high economic efficiency and less greenhouse gas (GHG) emissions in recent years. The efficiency of the CCHP system depends on the appropriate system configuration, operation strategy and facility size. Due to the inherent and inevitable energy waste of the traditional operation strategies, i.e., following the electric load (FEL) and following the thermal load (FTL), more efficient operation strategy should be designed. To achieve the highest system efficiency, facilities in the system should be sized to match with the corresponding operation strategy. In order to reduce the energy waste in traditional operation strategies and improve the system efficiency, two operation strategy design methods and sizing problems are studied (In Chapter 2 and Chapter 3). Most of the improved operation strategies in the literature are based on the ''balance'' plane, which implies the match of the electric demands and thermal demands. However, in more than 95% energy demand patterns, the demands cannot match with each other at this exact ''balance'' plane. To continuously use the ''balance'' concept, in Chapter 2, the system configuration is modified from the one with single absorption chiller to be the one with hybrid chillers and expand the ''balance'' plane to be a ''balance'' space by tuning the electric cooling to cool load ratio. With this new ''balance'' space, an operation strategy is designed and the power generation unit (PGU) capacity is optimized according to the proposed operation strategy to reduce the energy waste and improve the system efficiency. A case study is conducted to verify the feasibility and effectiveness of the proposed operation strategy. In Chapter 3, a more mathematical approach to schedule the energy input and power flow is proposed. By using the concept of energy hub, the CCHP system is modelled in a matrix form. As a result, the whole CCHP system is an input-output model. Setting the objective function to be a weighted summation of primary energy savings (PESs), hourly total cost savings (HTCs) and carbon dioxide emissions reduction (CDER), the optimization problem, constrained by equality and inequality constraints, is solved by the sequential quadratic programming (SQP). The PGU capacity is also sized under the proposed optimal operation strategy. In the case study, compared to FEL and FTL, the proposed optimal operation strategy saves more primary energy and annual total cost, and can be more environmental friendly. Finally, the conclusions of this thesis is summarized and some future work is discussed. / Graduate

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In the last decade there has been a significant increase in interest in microgeneration technologies for electric power. Sources of hydraulic power generation, wind and solar technologies represent some of the important developments that have had arising from the research efforts aimed at this area of power generation. The reason for this interest is due to the consolidation of what is called future in terms of power generation, which is based on decentralization of power generation through interconnected centers of small generators / consumers. At distribution level, distributed generation sources, together with the loads connected to its bus, forms what is defined as a microgrid. Depending on the instantaneous load and installed generation capacity, a microgrid can behave as a point of consumption or generation of energy at different times, being able to operate also connected to the network or islanded form according to the quality energy supplied or need in case of system failure. Among the technologies of microgeneration, micro hydro power plants with selfexcited induction generators (SEIG) came to represent an excellent option for electricity generation in isolated areas, mainly due to its characteristics of robustness and low cost, compared to synchronous machines. It is an alternative to the use of synchronous generators in low-power systems powered by small hydroelectric plants, rich in our country. In this sense, this Master's thesis deals with the modeling and control of a micro hydro power plant with SEIG with frequency and voltage control. The frequency control is achieved by controlling the opening of the feeding system of the turbine while the voltage control is performed through the control of reactive power of the set, using for this a Pulse Width Modulated (PWM) inverter. 10 Based on these definitions and knowledge acquired, it was proposed a system to be implemented experimentally, consisting of a micro hydro power plant, in this case a motor driven by a voltage PWM inverter, emulating the behavior of a turbine coupled to the induction generator. The terminals of the SEIG feed a bus where loads with different characteristics are connected, featuring a microgrid, having as main goal the control of the voltage and frequency stability of the energy supplied by the generator to the isolated system. Among the studies developed for the implementation of the prototype is possible to highlight: three-phase system modeling, hydraulic system modeling, voltage and frequency control, and synchronization method. Throughout this paper, simulations and experimental results are presented in order to be demonstrated the applicability of control methods, their performance and technical feasibility of the system. / Na última década houve um aumento significativo no interesse em tecnologias aplicáveis a microgeração de energia elétrica. Fontes de geração de energia hidráulicas, eólicas e solares representam algumas das tecnologias que tiveram importantes evoluções decorrentes dos esforços em pesquisas destinados a esta área de geração de energia. A razão para tal interesse se deve a consolidação do que é chamado futuro em termos de geração de energia, sendo este baseado na descentralização da geração de energia através de redes interligadas de pequenos centros geradores/consumidores. A nível de distribuição, as fontes de geração distribuída, juntamente com as cargas conectadas ao seu barramento, formariam o que é definido como uma micro-rede. Dependendo da carga instantânea e da capacidade de geração instalada, uma micro-rede pode comportar-se como um ponto de consumo ou de geração de energia em diferentes momentos, sendo capaz também de operar conectada à rede ou de forma ilhada de acordo com a qualidade da energia fornecida ou necessidade do sistema em caso de falta. Dentre as tecnologias de microgeração, as micro centrais hidrelétricas (MCH) com geradores de indução auto-excitados (GIAE) passaram a representar uma excelente opção para a geração de energia elétrica em áreas isoladas, devido basicamente as suas características de robustes e baixo custo, quando comparadas às máquinas síncronas. Trata-se de uma alternativa ao uso de geradores síncronos em sistemas de baixa potência acionados por pequenos aproveitamentos hidrelétricos, ricos em nosso território nacional. Neste sentido, a presente Dissertação de Mestrado trata da modelagem e controle de uma MCH com GIAE com controle de frequência e tensão. O controle de frequência é obtido a partir do controle de abertura do sistema de alimentação da turbina enquanto que, o controle de tensão é realizado a partir do controle da potência reativa do conjunto, utilizando para isso um inversor de tensão. Partindo destas definições e dos conhecimentos adquiridos, foi proposto um sistema a ser implementado experimentalmente, composto de uma micro central hidrelétrica, neste caso um motor acionado por um inversor de tensão, emulando o comportamento de uma turbina hidráulica, acoplado ao gerador de indução. Os terminais do GIAE alimentam um barramento onde são conectadas cargas com características distintas, caracterizando uma micro-rede, tendo como objetivo o controle da estabilidade da tensão e frequência da energia fornecida pelo gerador ao sistema isolado. Dentre os estudos desenvolvidos para a implementação do protótipo é possível destacar: modelagem do sistema trifásico considerado, modelagem do sistema hidráulico, controle de tensão e frequência e método de sincronismo. Ao longo desta dissertação, resultados de simulações e experimentais são apresentados, a fim de que, seja demonstrada a aplicabilidade dos métodos de controle, seus desempenhos e a viabilidade técnica do sistema.