Research On Adaptive Grid-Connection Control Of Converters For Direct-Driven Permanent Magnet Wind Generation System

Wind power is a green, clean, abundant energy. Due to the advantages of high operational reliability, low failure rate, low maintenance cost, direct-driven permanent magnet wind generation system has caused extensive concern. Combined with the research project "Modeling and Simulation on Adaption of Grid-Connection Technology for Wind Turbine" authorized by Electric Power Research Institute of Yunnan Grid, on the platform of PSCAD/EMTDC software, the stand-alone modeling technology, fault ride through technology, equivalent wind farm modeling technology, reactive power compensation technology of permanent magnet direct-driven wind generation system was researched in this paper.On the base of expounding the basic structure and the basic operational principle of permanent magnet direct-driven wind generation system, the mathematical model of permanent magnet direct-driven wind generation system was established, d-axis zero current vector control strategy for generator-side converter based on rotor flux orientation and control strategy for grid-side converter based on grid-side voltage orientation was analysised in detail,and correctness and effectiveness were verified by a simulation model.The influences of symmetric and asymmetric fall of three-phase grid voltage were analyzed in this paper. For the substantially symmetric fall of three-phase grid voltage, a control strategy providing reactive support and a protection scheme based on Crowbar overvoltage protection circuit were adopted to guarantee the safe operation of permanent magnet direct-driven wind generation system, also their correctness and effectiveness were verified by a simulation model. For the asymmetric fall of three-phase grid voltage, a control strategy for grid-side converter based on the separation of positive and negative sequence was adopted to suppress the second harmonic fluctuation of intermediate DC voltage, again the correctness and effectiveness were verified by a simulation model.The complete polymerization method for wind farm modeling and grouping equivalent method for wind farm modeling was researched. The conclusion that complete polymerization method has a higher accuracy than the grouping equivalent method was verified by simulation. Relationship between reactive power and grid-connect voltage of wind farm was analyzed, and the work principle of SVG was expounded. A simulation model was established to very the reactive power compensation capacity of SVG, and the simulation results showed that the addition of SVG could enhance the grid-connect voltage of wind farm effectively.