Research On Maximum Power Point Tracking Of Wind Turbine Based On Electromagnetic Coupler

With the increase of the installed capacity of wind turbines,its poor adaptive capacity of the traditional the wind turbine generator after the grid-connected is increasingly highlighted.To solve the problem,variable speed wind turbine in which synchronous generator is directly coupled with grid has been proposed in recent years.This thesis will to our country independent research and development of electromagnetic coupling type speed wind turbines as the research object.The variable speed wind turbine based on electromagnetic coupler(WT-EMC)developed by our country will be the object of study in this thesis.On the basis of analyzing the operating principles and running processes of wind turbine and electromagnetic coupler,the research content aimed at the maximum wind power tracking control and the speed closed-loop control in constant region.The main achievements are as follows:Firstly,this thesis introduces the development status of the wind power industry and summarizes the tendency of wind power technique in the future.The strengths and weaknesses of DFIG and PMSG are compared and analyzed.Then the running characteristics and research status regarding several different types of wind turbines are illustrated.These advanced wind turbines include switch reluctance generator,high voltage permanent magnetized generator,and magnetic gear integrated generator.It gives detailed descriptions of research actuality of front-end variable speed wind turbines that adopted different speed controllers such as Win Drive hydraulic torque converter,Chap Drive hydraulic transmission system,differential gear box and electromagnetic coupler.Secondly,the components of WT-EMC are elaborated.The mathematical model of electromagnetic coupler is established in dq and mt coordinate systems in terms of its composition structure and working principles.Combined with the working principle of electromagnetic coupler,the torque characteristics of wind turbines in the maximum wind power tracking area,constant speed area and constant power area are detailedly expound.Then,the principle characteristics of several kinds of MPPT control algorithm and their advantages and disadvantages are concluded separately.These algorithms incorporate the optimal tip speed ratio method,the power signal feedback method,climbing search method and the optimal torque method.In the case of ignoring the mechanical loss of the transmission shaft system,the optimal torque control method and speed closed-loop control are respectively applied in maximum power tracking area and constant speed area to build a simulation model of a variable speed wind turbine based on an electromagnetic coupler in maximum power point tracking.The simulation results,which are accomplished in step wind and random wind condition of the above two regions and their transition region,indicate that the wind turbine regulated by the optimal torque scheme using PI controllers can track the changes of wind in different working area.But this control algorithm can't make the wind turbine running accurately in the working state of the optimal tip speed ratio.It reduces the wind energy efficiency of wind turbines.Finally,in order to improve the efficiency of wind power utilization and optimize the wind power tracking control of wind turbines,backstepping sliding-model method combined with the optimal torque method is put forward.According to the theory of backstepping and sliding mode variable structure,speed backstepping controller and torque backstepping sliding-mode controller are respectively designed to apply in the constant speed area and the maximum wind power tracking area.A simulation model of WT-EMC in maximum power point tracking is built.The proposed control method has a simple structure and avoids measuring real-time wind speed.The simulation results,which are accomplished in step wind and random wind condition,indicate that this power tracking control scheme has good dynamic and static performance and better robust performance.Compared with torque backstepping and classical OTC,the proposed method can quickly and accurately track the variation of wind and effectively accomplish the goal of maximum power tracking.