Research On The Hvdro-Mechanical Hybrid Transmission System In Wind Turbines

With the new global climate agreement-the Paris agreement signed in 2015,renewable energy ushered another development opportunity.In all kinds of renewable energy,wind energy utilization technology should belong to the most mature rank,and its market and industrialization prospect are very bright.This paper studied from the wind turbine hydraulic mechanical hybrid transmission system working mechanism,scheme design and theoretical analysis,control strategy research,mechanical and hydraulic dynamics modeling and simulation to the semi-physical experimental verification.In summary,the paper completed the research on the hydro-mechanical hybrid transmission system in wind turbines.The contents of each chapter are as follows:The first chapter provides an overview of the wind energy utilization history and status,including the global installed capacity as well as installed capacity in China.Furthermore,wind power ratio of the total generating capacity is compared between Denmark and China to point out the gap.The wind turbine drive train classification and variable speed wind turbine technology research progress are reviewed.Furthermore,the defects of the current hybrid transmission structures are analyzed and the main research contents are proposed based on the research significance and the source.In the second chapter,the design and control strategy of the hydro-mechanical hybrid transmission in wind turbines is proposed.The torque,speed and power flow of planetary gear are further studied,on the basis of which four hybrid transmission schemes are put forward and compared to select the optimal one.The mechanical system parameters of hybrid transmission system are designed and calculated combining with the traditional 1.5 MW wind turbine.In order to improve the system transmission efficiency,closed hydraulic system is adopted and the key parameters are calculated.The control strategy for hybrid transmission system in different working conditions is analyzed,which can be elaborated as the optimum impeller speed control before/after grid connection below the rated wind speed,constant speed variable torque control above rated wind speed and the constant power control above rated power.Based on the mathematical model of the hybrid power transmission system,the power split/merge control,variable speed control and torque control are theoretically verified and analyzed.In the third chapter,the simulation parameters are calculated on the foundation of the 1.5 MW conventional wind turbine,and the joint-simulation is conducted using the advanced modeling software AMESim and commercial mathematical software MATLAB.Theoretical analysis and mathematical modeling of the wind speed,impeller,variable pump displacement adjustment mechanism,hybrid drivetrain,synchronous generator and the infinite power system are carried out in this paper.The 3-D model and virtual assembly of the wind turbine planetary gear flexible pin are constructed using the Ansys Workbench software,as well as the numerical simulation analysis on strength,bending stress and strain.Through the analysis of simulation results,it can be concluded that the stress and strain of the flexible pin can meet the design requirements and the control strategy achieves the maximum power capture below rated wind speed,mechanical structure protection above rated wind speed,and mechanical power stabilization while hydraulic system absorbs torque fluctuation above rated power.In chapter four,the 30 kW hybrid transmission wind turbine is designed and model selected,including the mechanical gear box,closed loop hydraulic system and electric control system.The key parameters of the mechanical gearbox and the closed-loop hydraulic system are calculated and the 3-D model of the hybrid transmission system are drawn.Besides,the preliminary debugging of the variable displacement pump is conducted to verify the linearity of the input voltage and output current.In chapter five,the 30 kW hybrid transmission wind turbine test bench is built,and the schemes of no-load test,load variable speed test,load torque absorption test,efficiency comparison test,torque absorption comparison test and grid connection test are put forward and the results are discussed.The experimental results show that the hybrid transmission wind turbine has eminent transmission features of variable speed control and torque absorption,and the mechanical and hydraulic power are reasonably splited.The novel transmission mode of mechanic transmits power while hydraulic regulates fluctuation is realized,and the electrical system successfully connects to the grid without frequency converter.In brief the wind turbine test bench accomplished all the designed objectives.The sixth chapter summarizes the main work of the paper,expounds the research conclusions and innovation points,points out the deficiencies of the paper and prospects the follow-up research work.