Research Of Wind Turbine Grid Voltage Fluctuations And Flicker Characteristics

In recent years,it was paid more and more attention to the problems of power quality by people.With the enlargement of the scale of grid-connected wind turbine,voltage fluctuation and flicker caused by grid will have a major impact on the security of the grid such as lights flashing and shadow rotation,etc.Voltage fluctuation is the phenomenon of voltage RMS value relatively rapid changes or continuously changes.Flicker is the harmful result caused by voltage fluctuation,that is the visual experience of the person to illumination fluctuations.At present,the research of power quality on grid-connected wind power mainly focused on problems such as harmonic,unbalanced three-phase power.Study on characteristics of voltage fluctuation and flicker is less,as well as flicker detection methods.Currently widely used IEC detection method is applicable to detecting the voltage flicker of electric arc furnace and other equipment.However,voltage flicker detecting results by using IEC detection method for grid-connected wind turbine in low frequency are always inaccurate.Therefore,in this paper,on the basis of IEC flicker detection method,voltage fluctuation and flicker characteristics of grid-connected wind turbines is studied by using the improved method.Firstly,this paper introduces the concept of voltage fluctuation and flicker,the causes and harm,and the suppression method.Then,explains the flicker detection methods and characteristics.Secondly,in view of IEC method,by increasing the parameter correction link to reduce the detection error in low frequency;Detecting the S(t)of the fluctuation voltage in low frequency by using the improved method.At the same time,in order to find more accurate method,using empirical mode decomposition(EMD)for detecting the same low frequency fluctuation voltage.It is concluded that the EMD method is more accurate,however it is also more complex.Finally,models of grid-connected wind turbine under the conditions of the basic wind and wind shear effect and tower shadow effect have been established by Simulink software,simulating and analyzing wind turbine output characteristic under different wind conditions.Then using the improved IEC method to test voltage flicker of grid-connected wind turbines.It is concluded that the influence of wind shear effect and shadow effect on flicker features of grid-connected wind turbine cannot be ignored.