الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Grid-tied inverters are at the heart of today’s renewable energy conversion systems. These inverters convert the energy harnessed from the various renewable energy sources, such as wind, sun …etc... Into a grid complied AC power that can be fed into the utility grid. The interfacing inverters inject power into the grid as long as the renewable sources are active (i.e. if sun is out and wind is blowing). However, if the renewable sources are not available, such as during night hours in the case of photovoltaic (PV) systems, inverters will remain idle. This reduces the effective utilization of these inverters. One way to increase the effective utilization of these inverters is to operate them as reactive power (VAR) compensators to generate reactive power whenever the renewable sources are not available. As the number of grid- tied inverters increases, their usage as flexible reactive power compensators will significantly help in grid voltage regulation and reduce the need of expensive capacity banks. Interfacing inverters could be employed to operate as active power filters. However, these special designed active filter inverters are not suitable for grid-tied applications. It will be interesting to enable existing grid-tied inverters to operate in reactive power generation mode in the absence of active input power. Actually, active power is required to power the control circuitry, compensate for the inverter losses, and maintain a regulated DC bus voltage. When active power is unavailable, the challenge is how to pre-charge DC bus and keep it regulated within limits while injecting the desired level of reactive power into the grid. If the inverter is to merely operate in reactive power mode, it needs to compensate for its internal losses and keep its DC bus voltage within an acceptable range. This thesis will provide a modified control strategy that enables PV inverters power control strategy to absorb modest active power from the grid when the renewable source (e.g. sun) is unavailable to compensate for the inverters’ internal losses, regulate DC bus voltage to keep it within limits, and operate the Abstract v inverters in VAR injection mode. PV interfacing inverter along with DC link is properly controlled to operate in static synchronous compensator (STATCOM) mode during night time to provide dynamic reactive power compensation and voltage support. The performance of proposed night control scheme is examined in MATLAB/SIMULINK environment. An experimental prototype demonstrating the night operation of PV system components is implemented. Simulation and experimental results prove that developed control scheme for night-time operation of PV system components is a feasible technique, since it enforces voltage support and dynamic reactive power compensation. The severity of the experienced voltage DROP caused by extensive loading conditions is reduced when PV system with the developed control scheme is applied. This eventually extends the utilization of PV inverters beyond active power generation and helps improving grid stability and voltage regulation.