The Simulation Research Of Direct-drive Wind Turbine Three-level PWM Grid Inverter Based On60°Coordinate System

Wind energy is one of the green pollution-free renewable energy, has good pros-pects for development, more and more countries in the world pay attention to the useand exploit of wind energy. Currently, the mainstream wind turbine is double-fedwind turbine and permanent magnet direct-drive wind turbine. In permanent magnetdirect-drive wind turbine, the rotor of permanent magnet synchronous generator isdirectly driven by the wind turbine. Compared with the double-fed wind turbines,permanent magnet direct-drive wind turbine has lower speed and higher number ofpoles, eliminating the liter-speed gearbox, with higher reliability, lower noise andlower maintenance costs, rapid development in recent years. Wind power grid con-verter system is to transform the electrical energy of variable frequency and voltagefrom the wind generator side to the AC electrical energy of constant voltage and fre-quency constant voltage, and then fed into the grid, it also can improve the powerfactor grid harmonic system, is an integral part of the wind power generation sy stem.With the gradual improvement of the unit capacity of today’s wind turbines, gridconverter technology is also a key link of the wind power technology and it largelyaffected the speed of the wind turbines stand-alone expansion and quality ofgrid-connected wind power.The thesis mainly based2MW permanent magnet direct-drive wind turbine con-verter technology, compared and discussed based on the SVPWM control strategies ofthe three-level network topology on the machine side rectifier and the network side ofthe inverter, analysis the capacitor midpoint potential reasons for the imbalance andproposed a solution, designed a LCL filter of the converter, verify the correctness ofthe model and control strategy through simulation.The paper first describes the background and significance of wind power, andelaborated the status of development and the trends of wind power technology, ana-lyzed several permanent magnet direct-drive wind turbine converter system. Subse-quently, detailed the structure of the direct-drive wind power system and the main partof the working principle; analyzed the power characteristics of the wind turbine andestablished mathematical model of wind turbine and direct-drive permanent magnetsynchronous generator. Then analysis the structure and characteristics of the maincircuit of three-level PWM grid inverter system, focus on analysis of the three-levelPWM control strategy grid inverter system, then detailed analysis the SVPWM algo- rithm based on a60°coordinate system, and compared with the traditional three-levelSVPWM algorithm; designed the LCL filter of network side. Finally, based on theparameters of the2MW direct-drive wind turbine and established a permanent magnetdirect-drive wind power system simulation model in Matlab/Simulink software.Comparative analysis the simulation results of two SVPWM control algorithm underthe maximum average wind speed, reflects the dynamic characteristics of the modeland verify validity of60°coordinate system based SVPWM algorithm and has a cer-tain value in engineering.