The Research On Asymmetric Low Voltage Ride Through Of DFIG

With the increase of installed capacity of wind turbine,The propotrion of energy systemare more and more large.So the requirement of the power grid across to wind turbine is higherand higher,when the power grid fault occurs,the wind turbine is still work on the gird,andprovide frequency and voltage to help power grid restoration compared with the traditionalpower generation techology.So the wind turbine must have LVRT ability.but because theprobablity asymmetric drop of power grid occur greater,So the research of wind turbine isfrom still work on the grid as the grid occur symmetic drop to occur asymmetric drop.This paper use the DFIG as the research object,because DFIG have large proportion.First,use DFIG work at the traditional control strategy,see the operation characteristics when thepower grid have asymmetic drop.From the simulation results we can see they have many twofrequency components,In order to suppress the two frequency components for researchpurposes.put out a method to solve this problem.And improve control strategy of the rotor andgrid side converter.When the power grid have asymmetic drop,Research on the rotor and grid sideconverter.get their math mathematical and instantaneous power model bellow on the positiveand negative rotary coordinate system.In order to improve the fault ride through capability ofrotor and grid side converter put forward three control objectives,And get the control strategyof this two converter use double dq、PI current regulator.but because when use double dq、PIcurrent regulator must decomposition the positive and negative sequence component,so theymust use notch filter when decomposition the positive and negative sequence component,Sowill cause delay on the current control loop,For this shortcoming, Design a proportional–resonant(PR)current regulator control strategy.The simulation results show this two kinds ofcontrol strategy is feasible.When the power grid have asymmetic drop,research on the LVRT of DFIG,First researchon the cooperative control of rotor and grid side converter.On the rotor and grid side converterspecify a control target,across thie cooperative control can reduce the two frequencycomponents as much as possible.After introduce the Crowbar protection circult.and researchhow to calculation the resistance value.last present two different measures when the powergrid have little fall and serious fall.when the grid have little fall the DFIG can use thecooperative control on rotor and grid side converter;but when the grid side have searious fall the must use a crowbar circult to protection rotor side converter.And last build a1.5MW DFIG model on MATLAB/Simulink,And simulator when thepower grid have little and terrible fall,the simulation indicate this time the DFIG can safethrough this period across the cooperative control of rotor and grid side converter,but whenthe power have terrible fall can very good to limit the rotor current when use crowbar circult.