Comparative Study Of Control Strategy For Direct-drive Wind Power Converters With PMSG

Energy is the material basis for the survival and development of human society.The conventional energy, such as coal, oil and natural gas, are not only restricted, butalso causing serious air pollution when they are burning. Thus, energy andenvironment are urgent problems for human survival and development today. As agrowing fastest, most nature technology owned and largest development renewableenergy, wind energy plays a particularly important role in the permanent magnetdirect drive wind power system especially. The gearless, low maintenance and lownoise make it attracts more and more attention., and it has became a importantdirectiom for future development of the variable speed constant frequency windpower system.In this paper, with the operation and control of the permanent magnet direct drivewind power converter as the theme, by using the topology and mathematic model oftwo commonly used control strategy: one is a control strategy using a uncontrolledrectify connecting a boost chopper circuit on the machine-side, and the other is thatcontrols power on the machine-side and bus voltege on the grid-side, the various partsof the system components are used to conducted a detailed mathematical derivation,then simulated. Based on two front control strategies, a novel control strategy areproposed, and the comprehensive comparison of simulation of three strategies aregiven, and not olny the comparative results are gained, but also the authentications ofthe last two strategies are introduced in the paper.At first, development status of wind energy and wind power generationtechnology research are introduced. Starting from the calculation of wind energy, thecharacterristics of the wind turbine are reserched, meanwhile, modeled and simulated.as the components of the wind power system for the converter, mathematical modelsof the PMSM, PWM converter and DC bus link are detially introduced. It makes abase for the future analysis.Second, first two control strategies are introduced in paper, one is a controlstrategy using a uncontrolled rectify connecting a boost chopper circuit on themachine-side, and the other is that controls power on the machine-side and busvoltege on the grid-side. Their theoretical analysis and simulation modeling arecarried out in detail. The first one uses the uncontrolled rectify on the machine-side, and the PWM converter on the grid-side. Not only the boost chopper circuit which isconnected to the uncontrolled rectify on the machine, and the corresponding controlstrategy, are analyzed and introduced, but also the PWM converter of the grid-sidewhich uses the voltage-oriented vector control strategy, is analyzed. The after one isDual-PWM converter. After analyzing the PMSM which is using the rotorflux-oriented vector control strategy, based on the relationship between power and thetorque current of q axis, the strategy which controls the power loop on themachine-side and still uses the rotor flux-oriented vector control strategy in the PWMconverter on the grid-side. And then, based on the two strategies, seen from theenergy conversion, a novel control strategy are gained by thinking reversely. Itcontrols the bus voltege on the machine side, and controls power on the grid side. Thesimulation of its model is given in the paper.At last, researched from three different perspectives such as the machine-sidecontrol, the DC bus link control and the grid-side control, the strategies mentioned inthe paper are compared by simulation, and differences of the simulink results arediscussed. It verifys that the strategies are correct and possible. In order to get a moredirect comparison, a comprehensive assessment of the overall control strategy is made,and corresponding conclusions are gained. And to describing the advantages of thestrategies directly, a comprehensive assessment of the overall control strateies areconducted. Seen from the results, the first strategy have a complex structure, and thequality of grid connected is poor, the efficiency is not high, but the cost of the systemis low, so it is suitable for small and medium-scale distributed generation systemwhich is less demanding on the quality of the grid connected. The structure of thesecond strategy is simple, and the quality of grid-connected is high, the efficiency ishigh, but the cost is also high, so it is suitable for the large-scale grid-megawatt powergeneration system. The last stratgy has same characters except the efficiency, itsefficiency is high. The results of the last two stratgeies show that the third one iscorrect and possible, and its efficiency is higher than the second one.