Research On Grid-Connecting Control Strategy Of Doubly-Fed Wind Power Generator

Energy is a focus of the current social attention. With the increasing demand of energy,the conventional energy cannot satisfy the energy demand of people. Human pay highlyattention to wind energy, which is renewable and green. The technology of wind powergeneration has been improved in recent years. The change of climate and the incentive ofpolicy make the prospect of wind power generation broader. Because of its superiorperformance, Doubly-fed Induction Generator (DFIG) becomes a powerful contender inthe wind turbine. So DFIG is selected as the research object.Firstly, the basic principle of DFIG is introduced. The equivalent circuit of DFIG andenergy flows of DFIG when it is in running states of super synchronous and synchronousare analyzed. The state equations are built according to the mathematical model of DFIG.3s/2s and2s/2r are introduced to simplify mathematical models that are high order, strongcoupling and nonlinear.Afterwards, how to control the converter of back-to back doubly-PWM is studied,which is the research emphasis of the paper. The analysis of rotor-side converter is basedon the vector control of stator flux, which realizes the active power decoupling control andreactive power decoupling control.The maximum wind energy tracking with DFIG isanalyzed, which makes the energy utilization rate of DFIG optimal.Secondly, grid-side converter based on voltage prompted vector control strategy isstudied. How to ensure the output of DC bus voltage is discussed. And how to guaranteethe supplement of active power and the reparation of reactive power by adjusting powerfactor are also discussed. Methods of generating PWM-waveform by adjusting duty factorand eliminating harmonics in the current by method of p-q are proposed. The two methodsare emulated to prove their validity and feasibility.Finally, experimental research of DFIG is designed. Schemes of hardware selectionand software programming for experimental platform are proposed. Grid-side andgenerator-side converters are emulated to prove the accuracy of the control strategy, which provides reference and foundation to the succeeding DFIG.