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Abstract
The ever-increase in energy consumption, limited amount of the conventional energy and the international needs to reduce global warming renders the search for new sources of energy. One of the vital components in the achievement of this goal is to provide a high share of energy obtained from renewable sources. Among these new sources of energy, photovoltaic power generation holds a particular promise as it is green, unlimited and is available worldwide. Though the photovoltaic phenomena was observed as early as 1839, it was not fully understood until the discovery of the quantum theorem early in the 1900’s. However, Lack of industrial tools and manufacturing technology delayed the development of solar cells production until the mid 1950’s when a solar cell was produced with efficiency less than 1%. Moreover, The need for solar energy in space industry was an important factor to initiate subsidies research activities in this area. However, the photovoltaic is recognized as an electric source for non space applications only after the oil crises in 1973. Intensive worldwide research plans over the last two decades led to a substantial development in photovoltaic industry. This appeared in the relatively high reduction of solar cell production cost, enormous increase in solar cell efficiency and producing solar cells that are able to extract photovoltaic power over the full spectrum of the wave lengths. Moerover, the idea of producing a photovoltaic plant that generates megawatts or connecting a photovoltaic system to the grid seemed unlikely to the most. Until the late 90’s, this is not the case at present as thousands of plants rated at more than 1 MWp( peak watt) are now in service. This up rating of photovoltaic generator a new era of photovoltaic energy utilization and the starting of an international a very large scale photovoltaic projects, including Egypt, have already been started.
One of the most important areas of photovoltaic application is the so-called stand alone energy systems, including water pumping and constant loads. This thesis presents the performance of a standalone photovoltaic system feeding constant and dynamic DC loads and controlled by a dc-dc Sepic or Cúk converter. Firstly, the mathematical model is obtained and a detailed nonlinear simulation is built to assess the system
performance with both converters. The system is built in the laboratory with a control circuit which enables the step up/down capabilities . To realize the performance of both the cuk and Sepic converters experimentally and test the simulation programs, the photovoltaic generator is replaced by a dc source and simulation and experimental results are obtained and presented in a comparative form. Extensive assessment of the performance of the photovoltaic system with both converters at different modes of operation are also presented and discussed. The results show operation at maximum power point can be achieved with both Cúk and Sepic converters without an extra maximum power point tracker by suitable adjustment duty cycle of the converter.
However, Cúk converter gives superior performance over Sepic converter over a wide range of operating condition. The results are presented in a comparative format illustrating wider range of the Cúk converter operation and forming a useful guide in designing a low cost stand alone photovoltaic systems .