abstract: In this thesis the performance of a Hybrid AC System (HACS) is modeled and optimized. The HACS utilizes solar photovoltaic (PV) panels to help reduce the demand from the utility during peak hours. The system also includes an ice Thermal Energy Storage (TES) tank to accumulate cooling energy during off-peak hours. The AC runs continuously on grid power during off-peak hours to generate cooling for the house and to store thermal energy in the TES. During peak hours, the AC runs on the power supplied from the PV, and cools the house along with the energy stored in the TES. A higher initial cost is expected due to the additional components of the HACS (PV and TES), but a lower operational cost due to higher energy efficiency, energy storage and renewable energy utilization. A house cooled by the HACS will require a smaller size AC unit (about 48% less in the rated capacity), compared to a conventional AC system. To compare the cost effectiveness of the HACS with a regular AC system, time-of-use (TOU) utility rates are considered, as well as the cost of the system components and the annual maintenance. The model shows that the HACS pays back its initial cost of $28k in about 6 years with an 8% APR, and saves about $45k in total cost when compared to a regular AC system that cools the same house for the same period of 6 years. / Dissertation/Thesis / M.S. Mechanical Engineering 2011

With the proliferation of residential-scale renewable energy sources and DC loads, it has become attractive to use residential DC electrical system that could offer benefits over the legacy residential AC electrical system. The Hybrid AC/DC house provides a sustainable alternative to preexisting residential electrical system by having both AC and DC buses. The DC bus facilitates the connection from DC sources to DC loads, whereas the AC bus interfaces AC sources to AC loads. The study develops the equations to calculate losses based on a model consisting of four main components: Multiple-Input Single-Output (MISO) converter, AC-DC converter, inverter, and DC-DC converter. Parameters such as AC and DC bus voltages, load consumption, and number of AC and DC branches were used to construct multiple scenarios and evaluate efficiency. Results of the study show that the Hybrid AC/DC house displays higher efficiencies than when the house has AC only sources with higher DC load consumption. Similarly, the Hybrid AC/DC house has better efficiency than when the house has DC only sources under higher AC load consumption. For the DC bus, results of the study further indicate that the higher DC voltage level yields better efficiency than those obtained from lower DC voltages.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This Master Thesis presents an AC Power Source (ACPS) study contribution through the proposal, design and implementation of a novel hybrid ACPS topology. In general, the proposed hybrid topology is defined from the series connection between a Modular Multilevel Converter (MMC), called main amplifier, and a Linear Power Amplifier (LPA), called correction amplifier. With this connection, the proposed ACPS enables the output waveform synthesis with high fidelity when compared to the reference waveform, also with a high bandwidth. The main contribution of the proposed topology is to allow the simplification of the main amplifier input stage, since the MMC requires a common DC bus for providing power to the load. Throughout this study, a linear amplifier DC bus design is presented, since it influences directly the ACPS performance. Regarding the main amplifier, dynamic models are presented for the control system design, which will ensure the circulating component minimization in the MMC poles, as well as ensuring the converter power flow balance by controlling the sum and subtraction of the capacitor voltages. Additionally, the pole inductors design considering the current ripple at the switching frequency is also presented. The ACPS prototype consists of eight half-bridge submodules, triggered by the control system implemented on a Digital Signal Processor (DSP) and through the selection algorithm implemented on a Field-Programmable Gate Array (FPGA). Finally, experimental results are provided in order to guarantee the employed methodology in the main and correction amplifiers design, through bench test prototype. / Esta Dissertação contribuiu com o estudo de fontes CA de potência (AC Power Source ACPS), através da proposta, desenvolvimento e implementação de uma nova topologia híbrida de ACPS. De forma geral, a topologia híbrida proposta é definida a partir da conexão série entre um Conversor Multinível Modular (Modular Multilevel Converter MMC), denominado amplificador principal, e um Amplificador Linear de Potência (Linear Power Amplifier LPA), denominado amplificador de correção. Com esta conexão, a ACPS proposta sintetiza uma forma de onda de saída com elevada fidelidade em relação à forma de onda de referência, juntamente com elevada banda-passante. A principal contribuição da topologia proposta é a possibilidade de simplificação do estágio de entrada do amplificador principal, uma vez que o MMC requer apenas um barramento CC para o fornecimento de potência à carga. No decorrer deste trabalho, também é apresentada uma análise para o projeto do barramento CC do amplificador linear, uma vez que o mesmo influencia diretamente no rendimento da ACPS. Em relação ao amplificador principal, são apresentados os modelos dinâmicos para o projeto do sistema de controle, que deve garantir a minimização da componente circulante dos polos do MMC, bem como garantir o balanço de potência do conversor através do controle da soma e da subtração das tensões dos capacitores das células. Adicionalmente, é apresentada uma análise para o projeto dos indutores dos polos em função da ondulação de corrente na frequência de chaveamento. O protótipo da ACPS é composto por oito submódulos meia-ponte, acionados através do sistema de controle implementado em um Processador Digital de Sinais (Digital Signal Processor DSP) e através do algoritmo de do balanço das tensões implementado em uma FPGA (Field-Programmable Gate Array). A partir da implementação da ACPS em laboratório, são apresentados os resultados experimentais com o propósito de comprovar a metodologia empregada no projeto dos amplificadores principal e de correção, bem como da estratégia de controle.