Two fuzzy logic controllers are proposed in this paper to control a three phase inverter for grid connected photovoltaic system. The first controller was used to predict the DC voltage that allows the three phase inverter to track the maximum power point of photovoltaic array under different environmental conditions such as irradiances and temperature. The second was used to control the active power and reactive power injected into the grid in order to inject the maximum active power produced by photovoltaic systems into grid with high efficiency and low total harmonic distortion using the same three phase inverter. The system components are photovoltaic array, DC link voltage, three-phase inverter, inverter control, LC filter, transformer and grid.  To verify the effectivnesse of the introdueced system, modeling and simulation are verified in Matlab/Simulink due to its frequent use and its effectiveness.

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This study presents a comparison of linear and nonlinear control to regulate the DC-link voltage and power factor correction of a wind farm equipped with squirrel cage induction generators (SCIGs), connecting to a 22-kV distribution network. Both active and reactive powers are employed in 2 independent control laws. The proposed control strategies are derived from the Lyapunov approach. The aim of the control is to maximize the generated power with the lowest possible impact in the grid voltage and frequency during normal operation and under the occurrence of faults.The nonlinear backstepping controller to be used for the control of the designed system is studied and compared with a classical proportional-integral controller for performance validation. The entire designed system is modeled and simulated using MATLAB/Simulink. Key words:Renewable energy, wind farm, squirrel cage induction generator, DC-link voltage control, power factor correction control, nonlinear control, backstepping approach, distribution network Wind farm connected distribution networkWhen large renewable energy sources are integrated into a distribution network, the dynamics and the operations of the network are affected [1]. The emergence of the smart grid will pose wind turbine (WT) developers with a new challenge: production during high wind speed, the value of the total harmonic distortion (THD), and power factor correction (PFC). The WT should be able to continuously supply the network. Among the technology choices, squirrel cage induction generators (SCIGs) are a very attractive choice for wind power generation because they are robust, inexpensive, and have low maintenance requirements and costs. As a network interface, the use of a back-to-back converter for speed operation is extensively reported in the literature, showing their capability to achieve maximum energy capture in a wide range of wind conditions [2][3][4].This renewable system generation has many uncertainties due to the erratic nature of wind-based systems. Therefore, the controller should accommodate the effects of uncertainties, keep the system stable against a large variation of wind speed, and produce good power quality. The conventional proportional-integral (PI) controller cannot fully satisfy stability and performance requirements. On the other hand, the wind power system is a highly nonlinear system and has a large range of operating points. Thus, linearization around one operating point cannot be employed to design the controllers. In this case, a nonlinear control method can be used to effectively solve this problem.

<span lang="EN-US">In this paper, a three-phase load connected to a NPC three-level inverter is presented. To generate gate signals for the multilevel inverter, two commands are developed and compared: the phase disposition pulse width modulation (PDPWM) and the space vector pulse width modulation (SVPWM). DC supply is provided by photovoltaic cells. Boost converter controls the power transfer from photovoltaic generator. Due to nonlinear I-V characteristics of photovoltaic cells, a maximum power point tracking algorithm is adopted to maximize the output power, the nonlinear controller (sliding mode) is developed and simulated. To verify the effectivnesse of the introdueced controller, it is compared with the fuzzy logic controller. Matlab-simulink is used for simulation, analysis and interpretation the results of these controllers.</span>