Research On Impedance Model And Resonance Damping Of Wind Power Generation System

At present,the global energy crisis and the environmental issue are aggravating day by day.Renewable energy,such as wind power,receives more and more attention.However,with the number of non-linear devices rising up,such as power electronic converters,the harmonic current increases continuously,which will occur parallel resonance under the action of the capacitor,transmission and distribution line in the wind farm.Sometimes the resonance can result in the phenomenon that the units detach the grid because of resonance voltage.The safe and stable operation of wind turbine is seriously affected.Therefore,studying the resonance suppression strategy has become a very important research direction in the field of wind power research.In this dissertation,main objects are the output impedance reshaping of Doubly Fed Induction Generator(DFIG)and its application in the suppression of wind power system resonance from three aspects:impedance modeling,resonance characteristic analysis,resonance damping.(1)The impedance model of DFIG-based wind farm composed is established.Firstly,the analysis modeling of DEIG is built,combined the modeling of machine-side,grid-side converter,and induction machine in abc coordinate system.Secondly,considering the transformer,the transmission lines and the wind farm topology(radial connection and trunk connection),the impedance model of wind farm is established.(2)Based on the impedance model of a wind farm,the influence of the number of wind turbines,the series/parallel virtual resistors on the resonant characteristics of wind farm is analyzed qualitatively by using the scanning results of wind farm impedance model under different conditions.(3)The resonance suppression strategy of wind power generation system under harmonic environment is studied.Including these aspects:1)Summarize the existing wind farm resonance suppression strategy,and analysis their characteristics and advantages/disadvantages comparatively.2)Propose a novel resonance suppression strategy that can reshape DFIG output impedance.First,the voltage/current components of the machine/grid-side converter are estracted.Then,the virtual impedance are added to adjust the reference voltage/current of machine/grid-side converters which will change the converters control signal.By controlling the signal of converters,the output impedance of DFIG is reshaped.When the reshaped impedance exhibits sufficiently large damping properties for the resonant frequency,parallel resonance can be effectively suppressed.3)Simulates based on PSCAD/EMTDC simulation platform,and compares traditional control method and resonance suppression method with virtual impedance added in the machine/grid-side converter.Verifies the correctness and effectiveness of the proposed resonance suppression strategy.