Research On Control Strategy Of Wind Energy Generation System Based On Doubly-fed Induction Generator

The study is focused on the doubly-fed wind power generation system and itsoperation control technology in this dissertation. Some key control technologies,such as vector control(VC), direct power control (DPC),maximum power pointtracking(MPPT),flexible cutting in and fault ride-through under unbalanced gridvoltage conditions were studies deeply from theory to practice and from simulationto experiment. The main research contents and conclusions are as followings:1.System structure of wind power generation based on Doubly fed inductiongenerator (DFIG) and its characteristics were analysised.The mathematical model forexcitation converter and DFIG were established under ideal grid voltageconditions.It provids the theoretical basis for the study on control strategy for DFIG.2.Vector control strategies for grid side converter (GSC), rotor side converter(RSC) and DFIG were studied. The vector control strategy based on grid voltageorientation for GSC was designed. The DFIG steady-state operation control strategybased on stator voltage orientation was adopted and its speed control mode andpower control mode were analyzed and compared. The feasibility of designedcontrol strategies were verified by simulation and experiment.3.Direct power control (DPC) for DFIG was studied. DPC based on hysteresiscontrol (HC-DPC) and DPC based on space vector modulation (SVM-DPC)strategies were comparing studied by simulation and experiment.4.Improved control method on power feedback MPPT control strategy wasproposed, DFIG stator optimal power-speed curve was obtained by experiment toavoid the complex calculation. Variable-step Hill Climbing Searching (HCS) controlalgorithm for MPPT was proposed, witch show a considerable independence of thefan parameters and air density. A new step algorithm in HCS was proposed to searchwind turbin’s optimum operation point more quickly and accurately. Experimentalresults show that the method is effective.5.DFIG no-load grid-connection control strategy based on grid voltageorientation was designed. The feasibility of designed control strategies are verified by simulation and experiment.6.Vector control strategy for DFIG under unbalanced network conditions wasstudied. Dynamic mathematical model of DFIG was derived in detail.Thedouble dq PI current control strategy based on the positive and inverse synchronousrotating coordinate and the proportional integral resonance (PIR) control strategybased on the positive synchronous rotating coordinate are designed. Simulationresults show that the two kinds of control strategies are effective under different gridvoltage failure and PIR control performance is better than that of double PIcurrent control strategy.6.The Experimental platform of doubly-fed wind power generation system wasset up.The experiment results shows that experimental platform can fulfill theoperation requirement of wind power generation system–based on DFIG.