Research On Grid-connected Control For Converter Of Direct-drive Wind Power Generator

The wind power generation has been drawn great attention of scholars in recent years, asone kind of effective use forms of renewable energy.With the advantages of high utilizationrate of wind energy, flexible grid-connected controllability and excellent system reliabilityetc., direct-drive permanent-magnet synchronous wind turbine system becomes the trend ofwind power technology research and development after doubly-fed wind power systems. Thisdissertation focused on the research for gird-connected control strategy of the full-scaleconverter in direct-drive wind power systems.Firstly, the algorithm for gird-connected inverter is analysed based on the space vectorpulse width modulation (SVPWM). The principle of space vector pulse width modulationalgorithm is analyzed in detail, and a method for judging the sector of the space vector andcalculating the time for composing the voltage vector is used, in which non-linear calculationsare avoided.Secondly, the approach for phase detecting of grid voltage for the grid-connected controlsystems is obtained, on the basis of phase-locked loop (PLL) technology. Basic principles ofPLL are summarized as well as conventional single synchronous reference frame softwarephase-locked loop (SRF-SPLL). In odder to solve the problem of the low accuracy and slowdynamic response when the SRF-SPLL is under grid fault, decoupled multi-synchronousreference frame software PLL is studied，and the PI parameter, dynamic response and steadystate error of SPLL is discussed.Then, establish the mathematical model of the grid-connceted converter and research thegrid-connceted control strategy. Mathematical equation of grid-connected converter isdeduced and direct-current closed-loop control strategy based on voltage orientation is studiedthrough the low frequency mathematical model of grid-connected converter in thesynchronous rotating dq refrence frame. The transfer function of current inner-loop andvoltage outer-loop is achevied by using decoupling control structure and the method of smallsignal linear analysis respectively, and the settings of PI controller parameters in the controlstructure are also discussed.Finally, acquire the simulation platform of the grid-connected control system withMatlab/Simulink/SimPowerSystems toolbox. The model is builded and the algorithm forinverter based on space vector pulse width modulation, the algorithm for phase detectionbased on decouple double synchronous reference frame software phase-locked loop and thegrid-connected control strategy is simulated. Meanwhile, a full-scale converters experimentaldevice which contains the diode rectifier, boost chopper circuit and the two-level voltage isdeveloped. The correctness and validity of the research is verified in this dissertation through theanalysis theoretical, simulation and experiment, which forms firm foundation both of theoryand practice for subsequent research.