Solar photovoltaic (PV) is one of the most promising renewable energy resources that converts solar energy into electricity with environment friendly manner. However, it has low efficiency and high relative costs. In order to overcome these drawbacks, a grid-connected PV energy system should be required to satisfy the load demand. The aim of this thesis is to study, design and performance analysis of grid-connected PV system as follows: • System modeling; that is composed of two-diode model to describe the I-V and P-V characteristic curves of PV system performance. Modeling of PV system represents the main goal in the design and performance study of grid-connected PV system using accurate parameters of PV module. Two-diode model with accurate seven-parameter is proposed to improve design, and predict optimum PV system performance at different irradiance and temperature levels. Seven-parameter is estimated using the Newton-Raphson method with the aid of initial values which are derived from basic equations of the model and manufacturing datasheet at standard test conditions (STC). The procedures were verified on three different modules of PV manufacturers using Newton-Raphson and Runge-Kutta Merson iteration methods. The results of proposed model show an excellent agreement with respect to datasheet and other related works at different irradiance and temperature levels. • Improving the efficiency of grid-connected PV system to operate at maximum power point (MPP) with the aid of perturb and observe (P&O) tracker via DC/DC converters. Although, P&O algorithm is widely applied due to its simplicity, costless and easy implementation, it suffers from instabilities, and oscillation around MPP at steady state. This thesis presents a modified P&O algorithm to overcome such drawbacks and improve MPP tracker (MPPT) performance of PV system under rapidly changes of weather. It uses a constant load technique to enable the P&O algorithm to track MPP at rapid-change of irradiance and other weather conditions. The modified P&O algorithm is simulated with a PV system and a DC/DC buck-boost converter to compare its results with other related works. Additionally, the proposed algorithm is simulated and experimentally validated using an 80W PV module, a boost converter and an embedded microcontroller. The experimental setup presents a model-based design (MBD) methodology that uses measurements’ data for MPPT systems’ design. It combines hardware-in-the-loop (HIL) simulation and prototype testing using actual weather measurements. The simulation and experimental results achieved maximum power tracking with high efficiency and minimum oscillations, better dynamic response, and stability for all weather conditions. • Investigating the design performance of grid-connected PV inverter that suitable for low voltage appliance of distributed grid network at 220V and 50HZ. This design includes sinusoidal pulse width modulation (SPWM) technique with series-resonance and high-pass filters at low side of inverter voltage to avoid resonance problem and reduce total harmonic distortion (THD). The inverter uses a new system of synchronous based on root mean square (RMS) of both inverter and grid voltages with adjustable phase shift leading angle of inverter to improve power factor. The Matlab/Simulink results shown excellent performance of 80W PV module.