| Severe environmental pollution and energy shortage forces people to develop new-type energy. Inexhaustible wind energy becomes a development item. Wind power generation is one of the most successful cases. Wind power generation has no pollution and occupies little land. Due to the fact that China started late on wind power, it lies a great gap between China and developed countries. The advanced technologies on variable pitch and variable speed control and the large size of China’s wind driven generator are still immature and most utility-type units are imported. China is a large country and has great demand for energy, so in-depth research of wind power generation is of great significance.Wind turbine generator system is a complicated, nonlinear and multivariable system, so wind generator system modeling is vital to research of wind generation. Owing to changeable wind, how to capture maximum wind energy and output power for wind turbines is a necessary problem to be solved. The paper conducts research of mathematical model of nonlinear wind turbine system model and control of maximal wind energy capture and variable pitch control. It primarily includes the following:(1) To study Betz Theory of wind turbines. Through analysis of air flow upstream and downstream energy change of wind rotors, it is confirmed that the energy wind turbines obtain from natural wind is limited. The amount of energy wind turbines obtain is related to tip speed ratio and pitch angle, i.e., rotor power coefficient. Then we receive aerodynamic characteristics of wind rotors and lay foundation for wind rotors modeling.(2) In order to make a more real and better account of natural wind change, the paper sorts wind speed into basic wind, gust, gradient wind and random wind as well as adopts the hybrid parameter model.(3) To establish a nonlinear system model of wind turbine generator system. The paper takes common horizontal shaft wind turbines as the research object, establishes a model by summarizing features of transmission chain layout form and makes it have generality. The paper sets up mathematical models of wind rotors, gear boxes and asynchronous generators and simulation models on Matlab/Simulink. Under different wind regime, the simulation of wind turbine generator system is conducted.(4) To study the control methods of capturing maximum wind energy for wind turbine generator system. The paper studies three strategies of maximal wind capture control and employs the tip speed ratio control method by comparison of merits and demerits and setting wind turbine parameters and the PID controller frequently used in industrial control as well as establishes simulation on Simulink.(5) To study variable pitch control of wind driven generator. It is proven that variable speed and pitch control is the best by comparison of without control and variable pitch control and their merits and demerits. The paper sets up a model that can be applicable to research of control methods and guidance of design of wind turbine generator system. |
