الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The trend towards the use of renewable energy sources as an alternative to conventional energy sources is constantly developing and increasing to overcome problems of world energy crisis such as the decay of fossil fuels and environmental pollution. The remarkable advantages of solar energy over the other renewable energy sources such as the absence of fuel cost, pollution free and low maintenance have made it one of the most promising energy sources. Photovoltaic systems suffer from low efficiency especially when the irradiation is suddenly changed. Hence, the Maximum Power Point Tracking technique (MPPT) is introduced to overcome this drawback. MPPT technique increases the overall efficiency of the PV system by actively extracting its maximum power under any operating condition. The Perturb and Observe method (P&O) is a very popular algorithm used to obtain the maximum power from a PV array. However, the conventional P&O algorithm cannot deal with shaded PV modules and fails to provide a high overall system efficiency. Using a small perturbation improves the PV system efficiency but increases the tracking time. On the other hand, a large perturbation causes higher oscillations with low efficiency. So, the conventional P&O algorithm has a trade-off between tracking speed and obtaining high efficiency. By improving the tracking of the maximum power point (MPP) with the new control algorithms, the PV power generation and overall system efficiency have been improved. In this thesis, an effective approach to extract the maximum PV power without using a DC-DC converter is introduced. The MPPT technique is used to directly control the PV load in order to extract the maximum power without controlling the duty cycle of the conventional DC-DC converters. The modified P&O method is used to generate the power reference directly to load inverter instead of controlling the duty cycle of the conventional DC-DC converter. However, the proposed technique can still use the conventional DC-DC converter scheme to regulate the inverter dc-link only. The modified MPPT provide the reference power to a closed loop power controller which generates the required pulses to the inverter through a conventional PWM modulator. ABSTRACT
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The proposed direct power control technique overcomes a trade-off between the tracking speed and obtaining high efficiency. The PV load is presented by a three-level Neutral-Point-Clamped inverter (3L-NPC). The inverter dc-link is regulated by a DC-DC Buck-Boost converter with a closed loop voltage controller. The proposed scheme enhances the inverter output wave quality by introducing a new technique which optimizes the inverter modulation index which is so-called Modulation Index Control (MIC). The MIC technique ensures optimum dc-link voltage which results in enhancing the inverter output Total Harmonic Distortion (THD). Finally, the overall proposed system including Direct Power MPPT and MIC control is verified through simulation and validated experimentally.