Maximum Power Tracking Of Doubly-Fed Induction Generator In Wind Turbine System

For the continuity of human to develop, we have to find renewable sources of energy. Even we find the coal and fossil fuel for hundreds or thousands of years. But what will happen after the depletion of these resources? Even the energy sources like fusion generate a large amount of waste heat. Global warming is increasing day by day; environmental pollution is another big problem. In 1995 US generated 3 trillion KW of electricity,70% of it was produced by fossil fuels. This causes the emission of 2 billion tons of CO2,15 million tons of SO2 and 6 million tons of NOx [71]. If we continue using these resources, then day will come when survival of humanity become difficult. We all are paying the price of these problems. There is popular underlying support for renewable energy sources, especially for wind power generation.During the last few decades, the concept of a variable-speed wind turbine (WT) has been receiving increasing attention due to the fact that it is more controllable and efficient, and has good power quality. As the demand of controllability of variable speed WTs increases, it is therefore important and necessary to investigate the different control techniques for wind turbine-generator systems (WTGS) that are capable of extracting the maximum power from the wind energy. Therefore, this thesis will provide details about wind energy, Maximum power point techniques of a grid-connected wind turbine system equipped with a doubly-fed induction generator (DFIG), which includes the aerodynamic models of the wind turbine, DFIG models and the three-phase two-level PWM voltage source converter control algorithms.In order to obtain satisfying output power from the WTGS, control strategies are necessary to be developed. These control schemes include the grid-side converter control, the generator-side converter control and the maximum power point tracking control. The grid-side converter controller is used to keep the DC-link voltage constant and yield a unity power factor looking into the WTGS from the grid-side. The generator-side converter controller has the ability of regulating the torque, active power and reactive power. The maximum power point tracking control is used to provide the reference values for the active power at the stator terminals.For maximum power point tracking tip-speed ratio method has been used. The main idea of tip-speed ratio method is that, if wind turbine turns so slowly then most of the wind will pass through the blades undisturbed and very little power will be extracted. On the other hand, if wind turbine will turn so fast, then it will appear as a wall for wind and no wind will pass though wind turbine. As a result it will again reduce the power extraction. To get maximum power from wind, the wind turbine should run at the optimum tip-speed ratio. The optimum tip-speed ratio depends upon the wind turbine design.In order to test the performance of the grid-side converter control, the generator-side converter control and the maximum power tracking, the wind turbine-generator system was simulated under a sinusoidal wind speed variation condition.