| Recent environmental policies and higher needs of energy have led to the huge growth in renewable sources consumptions. Consuming renewable energies however, is not always free of challenges. Many studies have been done to have a reliable integration and localization of the distributed sources, which have evolved into microgrid concept. These studies are mainly focused on microgrid's occurrence prediction methods, control schemes and their undeniable part, grid synchronization techniques. The main goal of the studies is to help the microgrid and their distributed sources to ride through the short disturbances in grid-connected and islanded modes. Disturbances and unplanned changes that occur to a microgrid result in voltage and frequency fluctuations. These fluctuations could have destructive effects on power equipments. Therefore the existence of a robust and reliable controller and synchronizer is a must in microgrids.;In this thesis, the focus is on synchronization techniques and control systems. Among different synchronization techniques including PLL-based methods and frequency adaptive methods, the Adaptive Notch Filter (ANF) is selected to be studied in more details. A controller design consisting of an ANF is then proposed to fixate the voltage and frequency of the system while islanded and to ensure the power generation sufficiency. Another important and critical task of the proposed controller is to prepare the islanded microgrid for transitioning to the grid-connected mode. The Fast and accurate synchronization technique is selected and a fast responding control system is proposed to achieve a smooth transition between the two modes.;The ANF synchronization technique along with the proposed PLL-less control design are modeled in Simulink/MATLAB, which their performances in a system with disturbances and occurrences are evaluated. Balanced and unbalanced loads are added to the system and the connection between the microgrid and the grid is established. In this thesis the accuracy of the proposed control system in different conditions is examined and simulation results are presented. The results show that balanced three phase voltages at a fixed frequency are achieved, which also ensures a smooth transition between two modes. |
