Research Of Wind Turbine's Grid Connection Testing Technique

With the rapid development of wind power industry,the whole capacity of wind power is so huge that the potential impact to grid cannot be neglect anymore.Most countries have raised grid codes for wind turbines and require the compulsory tests to wind turbines prior to connections to grid,such as power quality,LVRT and so on.And HVRT test is also a prerequisite in some countries.The ability of testing organizations is insufficient when they handling all kinds of wind turbines of different manufacturers.More and more manufacturers begin to construct grid connection test rigs by themselves to speed up research and development period of the products,as well as enhance the technique level of grid integration.Emphasize on LVRT test technique,this paper analyses several mainstream wind turbine strategic of LVRT principal,designs the hardware of test equipment that based on the theory of voltage divider by reactance.By different configurations between current limit impedance and short circuit impedance,test equipment is able to compose thousands of ratio to meet the turbines with different capacity and to apply to all kinds of grid structure.The acquisition system based on DEWETRON measuring devices can ensure the necessary accuracy of the measuring parameters.And propose a calculation method to evaluate the effect to the grid when the testing equipment connected in series to the medium voltage system.The traditional voltage dip testing equipment usually spent quite a long time to change the tap position of impedances to acquire different reactance values with wind turbine stopping,which lead to the power production waste dramatically.On the basis of regular LVRT testing machines,this paper proposes a new scheme characterized non-stop change taps technique by adding bypass breakers to medium voltage side.The advantages of changing impedances taps with turbine running lie in sparing operate time,increasing testing efficiency,especially reducing power production waste.Data disposing and analyzing of testing results is a key technique to the grid connection performance testing of wind turbines.Another key technique are the calculations from medium voltage,current,active power,reactive power collected by acquisition instruments to positive sequence fundamentals according to IEC standard.Based on the platform of Matlab/Simulink,this paper designed a calculation model of positive sequence fundamentals,which can calculate original testing data rapidly.The LVRT test case of large-size off-shore wind turbine validated the availability of the testing system designed,as well as validated the settings of grid protection parameters after calculating the different grid effect caused by different types of voltage dips.Testing data was disposed on the Famos software platform,based on which the results were displayed in the testing report finally.Otherwise,this paper designed remote surveillance system with 3G communication technique,by which the realtime status of wind turbine and testing machine were monitored remotely.This technique makes remote testing support possible,especially shorten LVRT period.