Research On Variable Pitch Control System Of Stand-Alone Wind Turbines

At present,the investment from government on wind power industry has been increasing.Large-scale construction of wind farm has led to climate change.Small and medium scale independent wind turbines could be an environmentally friendly option for the future of renewable energy.The structure and control method of existing small and medium scale stand-alone wind turbine were analyzed in this thesis.There are some disadvantages in existing wind turbines,such as the inadequate real-time control of rotor speed and the low reliability of wind turbine.In order to solve these problems,the structure and control strategy of stand-alone variable pitch wind turbine were studied,the model of small and medium scale stand-alone wind turbine system was built,and the simulation of the pitch control algorithm was completed in this thesis,as well as experimental verification.The work product mainly includes the following.This thesis analyzed the components of independent model of small and medium scale stand-alone wind turbine system,including wind wheel,transmission system,generator system,power electronic converter,variable pitch system,and energy storage system,etc.Operation characteristics of this wind turbine under different wind conditions were analyzed.Maximum Power Point Tracking methods were studied.Different actuators of variable pitch system and corresponding control methods were researched in this thesis.The mechanical transmission and signal transmission relationship of each part and others in stand-alone wind turbine were studied.This thesis built the models of these systems,including wind speed model,aerodynamic model,transmission system model,permanent magnet synchronous generator model,power conversion device model as well as the pitch-controlled system model.The maximum power point tracking control was simulated in case the rotor speed was under rated speed.Pitch control algorithm of the stand-alone wind turbine system was deeply studied in this thesis.PID pitch control algorithm and fuzzy PID pitch control algorithm were implemented and validated by simulation experiment.Experimental results showed that the rotor speed can be controlled at rated speed by both of the two controllers.But the overshoot and adjustment time of fuzzy PID controller were better than PID controller.Control system of the stand-alone variable pitch wind turbine was designed in this thesis.Rotor speed sensor,voltage sensor,current sensor,variable speed controller and actuator of variable pitch system were selected.Schematic and printed circuit board(PCB)of main controller were designed,used the chip of STM32,which based on ARM kernel.The pitch control and data acquisition system were programmed.Experimental platform of stand-alone variable pitch wind turbine was set up.Based on vehicle experiments with the platform,this thesis tested the software and hardware of variable pitch control system and obtained the rotation speed characteristic curve and power characteristic curve of the prototype.Based on the adjustment of the blade pitch,the generator speed and power can be controlled in rated ranges.The dynamic characteristics of the rotor speed can meet the control requirements of small and medium scale stand-alone wind turbines.The results can be used to implement real-time control of rotor speed and generator power,in the small and medium scale stand-alone wind turbine,can improve wind energy power coefficient.And can promot the reliability and stability of whole system.