The Modeling And Control Of DFIG-based Wind Turbine

With As a result of energy crisis and environmental awareness, wind power generation as a kind of renewable and clean energy attracts broad attention recently. DFIG- based wind turbines have become the most dominating type of yearly installed wind turbines because of their attractive features. The back-to-back power converter connected to rotor makes DFIG-based wind turbines controllable for maximum power tracing and meeting requirement of utilities.Traditional synchronous generators possess inertia which responses with utilities frequency because of the relationship between utilities frequency and rotor speed. However, existing DFIG-based wind turbines is controlled by exciting currents of rotor. The back-to-back converter isolates the utilities frequencies and rotor speed. Therefore, with the penetration of wind turbine increasing, inertia of grid will decrease, which might leads to stability reduction of power system. In order to popularize wind power generation, those key issues need to be solved and optimized. This dissertation concentrates on effectively utilizing wind power and flexibly adjusting output active power of DFIG-based wind turbines according to grid state.The dissertation is organized as follow: Firstly, general introduction to the development of wind power in China and Abroad, current situation and trend of the development of wind power technology. Secondly, basic knowledge and basic operation principles of DFIG-based wind turbines are introduced. Thirdly,this dissertation respectively explains the mathematic model of electrical section, mechanical section, back to back power converter and DFIG controller section. Most important, according requirements, control strategies of DFIG-based wind turbines for maximum power point tracing and virtual inertia are obtained. Which makes DFIG-based wind turbines can both utilize wind power effectively and generate virtual inertia to resist utilities frequency fluctuation by releasing or accumulating kinetic energy of wind turbines. Rotor speed can be appropriately adjusted according to both wind speed and utilities frequency. Finally, those control strategies are tested in MATLAB/Simulink. The result of simulations proved the control strategies is effectual for maximum wind power tracing and utilities frequency response.