Research On Optimization Of Pitch And Torque Control Of Front-end Speed Controlled Wind Turbine

Using synchronous generator and hydraulic torque converter speed control system, the front-end speed controlled wind turbine has characteristics of outstanding low voltage crossing ability, high reactive power output capability, good power quality and reliability. The front-end speed controlled wind turbine is gradually becoming mainstream model for the future development of wind power technology. Therefore, it is important for the promotion of development of wind power technology to research on related content of the front-end speed controlled wind turbine, such as the power control, the torque converter speed control and the optimal control of pitch and torque system.In this thesis, the front-end speed controlled wind turbine as the research object, it is focused on the working principle of the front-end speed controlled wind turbine by analyzing turbine structure and guide vane adjustment mechanism, and then on this basis, according to the research questions, a mathematical model is built for main components of the front-end speed controlled wind turbine.Secondly, variable pitch control theory of the front-end speed controlled wind turbine is researched. On the basis of aerodynamic characteristics analysis and wind wheel model, the theory of maximum wind energy capture below the rated wind speed and the theory of power limitation above the rated wind speed are analyzed and explained. Aiming at active power control problem above the rated wind speed for the front-end speed controlled wind turbine, the controller for active power is designed based on genetic algorithm, and is analyzed by building control system simulation model. The simulation results shows that the designed controller effectively achieve control objectives for turbines of constant output power.Thirdly, hydraulic torque converter speed control theory of the front-end speed controlled wind turbine is researched. Analysis is expanded about regulating process of torque converter speed control system which is input with variable wind speed and output with constant revolving speed. According to the working principle and the governor characteristic of hydraulic torque converter with Adjustable guide vane, the fuzzy controller is designed based on self-tuning of the dual mode parameters, and is analyzed by building simulation model of hydraulic torque converter speed control system. The simulation result shows that the turbine output speed is stably in the vicinity of its rated speed, and that the control effect of guide vane for the torque converter is obvious.Finally, aiming at power control problem above the rated wind speed for the front-end speed controlled wind turbine, a power optimal control strategy is proposed based on differential evolution algorithm. The objective function for torque converter speed control system is established with the goal of constant output revolving speed and smoothing output power. Using differential evolution algorithm, two control parameters are optimized, that are the pitch angle of the pitch system and guide vane angle of hydraulic torque converter speed control system. According to the optimized parameters, wind turbines are under control with variable pitch and torque, in order to achieve optimal control for output active power of turbines. Taking 2MW front-end speed controlled wind turbine as research object, which is power controlled using the proposed method in this thesis,the simulation results of control policy verification analysis shows that output power of wind turbine was smoothed and the power fluctuation was reduced, in which way, the feasibility of the control strategy was verified.