Research On The Low Voltage Ride Through Technology Of Grid-connected Power Conversion For Directly-driven Wind Generation System

This dissertation mainly focuses on the research and simulation of the control strategy of the grid-connected conversion of the directly-driven wind generation system for running under grid fault. Mainly includes the following:The first, the fundamental research:includes the basic principles of three phase voltage source PWM inverter and permanent magnet synchronous motor, the mathematical model of PWM inverter under Three-phase static coordinate and two-phase synchronously rotating coordinate and the mathematical model of PMSG under two-phase synchronously rotating coordinate.The second, makes an analysis and summary of the control strategy of the grid-side and motor-side converter, mainly put emphasis on the voltage-oriented vector control strategy of grid-side converter and the rotor flux-oriented vector id=0 control strategy of the motor-side converter. Then, makes an analysis of the control strategies of the DC-side power consumption circuit, a reactive power control strategy under LVRT in grid-side converter is proposed. Finally, a new control strategy which the motor-side converter emphasizes on the regulation of the dc-link voltage is proposed.The third, a simulation model of a 1MW PMSG back to back PWM inverter is built, and based on it, those control strategies which mentioned previously got verified. Finally, a VSG(Voltage Sag Generation) based on the form of impedance is designed and built. A 100kW DFIG experimental platform has done LVRT experiments with it.