The Through Operation Of Squirrel-cage Asynchronous Wind Power System Under Unbalanced Grid Voltage

With the increasing shortage of fossil energy and the protection of the ecological environment,the new national energy policy points out that it is necessary to develop and speed up the development and utilization of wind power.Wind power has developed rapidly in recent years,the proportion in power grid in China is increasing,the impact on the grid has become more obvious.In order to maintain the safe and stable operation of the power grid,the new grid connected national standard clearly points out that the grid connected wind farm and wind turbine must have the ability of low voltage ride through.The squirrel cage induction generator(SCIG)has the advantages of simple structure,easy manufacture,low cost,reliable operation,convenient maintenance and suitable for harsh environment,which has been paid more and more attention in the wind power generation industry.In addition,multi models of wind farm can improve the stability of wind farm.This paper focuses on the SCIG,study a full power driven cage type asynchronous wind power system.The main work is as follows:(1)Introduce the overall structure and main system of the cage type asynchronous wind power system.Study and establish the mathematical model of the wind turbine,describe the maximum wind energy capture technology,and introduces several ways to realize the maximum wind energy capture of the system.The mathematical model of SCIG in the two-phase synchronous rotating dq coordinate system is deduced in detail,analyzes the work characteristics and operation principle of double PWM,and also deduces its mathematical model,which lays the foundation for the research of the control strategy of the system.(2)Analyzes the theory of drive and control technology of asynchronous generator,the vector control strategy based on rotor flux orientation is discussed in detail;In addition,a weak magnetic control strategy based on the stator voltage closed loop is proposed based on the analysis of the operating characteristics of the wind turbine above the rated speed.Through the Matlab/Simulink simulation software,the SCIG's drive control technology is modeled and simulated.(3)Study the working principle and operation characteristics of the SCIG driven by full power converter.Based on the mathematical model of the SCIG,a steady state control strategy is studied.And through the Matlab/Simulink simulation software,the system is simulated and analyzed,and the feasibility of this control scheme is verified.(4)Analyzes the operating conditions and the power transmission characteristics of the cage type asynchronous wind turbine driven by full power converter under unbalanced grid.In this paper,the DC side add the chopper to prevent the DC bus voltage from soaring under unbalanced fault.Two control strategies are proposed based on the proposed method:1)The vector control strategy of the double current loop based on the positive and negative sequence voltage orientation;2)The current control strategy of quasi PR controller is adopted in the two phase stationary coordinate system.Analysis deeply and derive the two control strategies,and then use the MATLAB/Simulink toolbox to buildrespectively the simulation models of two kinds of control strategy,and do the simulation under three different control objectives.