Control System Research Of Full Power Grid-connected Dual PWM Converter For Direct-drive Permanent-magnent Wind Power System

In recent years, the direct-drive permanent magnent wind power system has got great development. As an important component of the wind power system, the converter is the key to invert wind energy to excellent grid-connected electrical energy. Now related converter equipments depend on importing in our country, converter control has also big gap between our country and some foreign countries whose wind power technologies are advanced, especially for the dual PWM converter which is used more and more. The main contents are below.(1) Mathematical models of direct-drive permanent magnent wind power system including permanent magnet synchronous generator (PMSG) model and dual PWM converter model are built. Space vector pulse width modulation (SVPWM) control technical is adopted by the dual PWM converter. By using SVPWM control technical the dual PWM converter has advantages of a high DC side voltage utilization ratio, little switching loss and a low output current harmonics amount.(2) Control strategies of the dual PWM converter including generator-side PWM converter control strategies and grid-side PWM converter control strategies are researched. Generator-side PWM converter uses double closed loop control strategies of outer speed loop and inner electric current loop, grid-side PWM converter uses double closed loop control strategies of outer voltage loop and inner electric current loop.(3) PMSG simulation model, the dual PWM converter simulation model, grid simulation model and grid-connected simulation model of direct-drive permanent magnent wind power system are built in the MATLAB/SIMULINK simulink envirement.(4) In view of low-voltage-ride-through (LVRT) capacity of direct-drive permanent magnent wind power system, the method that unloading circuit is added in the DC side and static synchronous compensator (STATCOM) is used in the grid side to the grid is used to improve system LVRT capacity.(5) On the basis of the grid-connected simulation model, corresponding unloading circuit simulation module and STATCOM simulation module are added in, and then system LVRT simulation model is built.Corresponding simulation parameters are designed respectively, simulation and analysis of system grid-connected performances and LVRT capacity is done. Results show that generator electromagnetic torque can be controlled exactly, DC side voltage maintains steady well, shapes of voltage and current into the grid are close to the sine and the content of harmonics is little by using the dual PWM converter control strategies; When grid voltages dip unloading circuit limit DC side voltage increasing very well and STATCOM provides plenty of reactive power compensation to the grid.