Research On Power Ttransformation And Control Technique In Doubly-fed Wind Generation System

It is difficult to develop wind energy because of its randomness and intermittence.The doubly-fed induction generator(DFIG)in doubly-fed induction generator system can achieve variable speed constant frequency operation according to variant wind speed,which solves the problem of variant wind energy.It can also capture wind energy effectively and improve the efficiency of doubly-fed induction generator system extremely.In doubly-fed induction generator system,the electrical energy flowing through the converter is slip power(about 30% of rated power),which reduces the volume of converter effectively and makes DFIG have a strong practicality.Doubly-fed induction generator system is widely used for its high efficiency and practicability.This paper focuses on the research of power conversion and control technology in doubly-fed wind power generation system.Firstly,a mathematical model of DFIG in static coordinate system is established,which lays the theoretical foundation for the research content of this paper.Then,in the research of power conversion control technology based on PI controller,this paper establishes grid side converter control system and rotor side converter control system based on PI controller.The grid side converter control system is built by analyzing its mathematical model in rotating coordinate and according to two conditions of single-machine no-load generation and grid connected operation,different rotor side converter control systems are built respectively by analyzing their mathematical models in rotating coordinate.Next,this paper introduces the concept of proportional-resonant controller(PR controller)and introduces it into the doubly-fed wind power generation system using its superiority of tracking sine signal without static error,which eliminates the coupling term and feedforward compensation term in the control system and simplifies the control system structure.Moreover,the MATLAB/Simulink simulation indicates that the control system based on PR controller also has good control performance compared with PI controller control system.Next,the experimental platform of doubly-fed wind power generation simulation system is improved and the control system of rotor side converter is studied using the experimental platform.The experiment results shows that the rotor side converter control system based on PR control has good control performance during single-machine generation operation.Finally,this paper studies the output power of DFIG,designs and implements the device to convert the output of DFIG to the intermediate frequency AC power.