Study On The Low Voltage Ride Through Strategy Of Doubly Fed Wind Power Generator Under Asymmetric Faults

With the rapid development of wind power in the world,the installed capacity of wind turbines in power systems shares an increasing proportion day by day.In the wind power generation system,variable speed constant frequency doubly-fed wind power generator has advantages of control flexibility,wide range of speed and small capacity of the needed excitation converter,so it has become the mainstream wind model in the wind farm.O wing to the limitation of its structure,the control ability of doubly-fed wind power generator is easily affected by power grid failure.Consequently,how to improve the Low voltage ride through capability of doubly-fed wind power generator has become a research focus in the wind power industry.Basing on the mathematical model of doubly-fed wind power generator under the asymmetric power grid fault,this paper carries on the detailed discussion on the improvement of the doubly-fed fan low voltage ride through technology.The main contents are as follows:1?To set up the mathematical model of doubly-fed wind power generator in the three-phase static coordinate system and two-phase synchronous rotating coordinate system,simultaneously to have a modeling analysis for the network side converter,build the traditional control method of doubly-fed generator under asymmetric power grid fault and make a detailed analysis of various electric parameters of the traditional control method through the simulation.2?To make full use the fast reactive power adjustment ability in the rotor side converter and web side converter of doubly-fed wind power system,so as to make efficient support of terminal voltage during the fault.By discussing the conventional separation methods of the positive and negative sequence component of asymmetric vector in detail,this paper puts forward an improved method of positive and negative sequence separation and applies to the cooperative control in the rotor side converter and web side converter.To a certain extent,it improves the low voltage ride through capability of doubly-fed wind power generator3?To analyze the mathematical model of the web side converter in detail.O n the basis of this analysis,this paper designs a first order LADRC(Linear Active Disturbance Rejection Controller,LADRC)as a voltage loop controller.It makes the high power factor of system operation.Using the specific mathematical model which is completely independent of controlled object and the characteristics of strong ant i-interference ability of LADRC,we make the system as a whole ha ve a good compensation accuracy and anti-interference characteristic.Because that the first-order LADRC is a feedback system,its nature is the stability of the system.This paper uses classical control theory to prove the stability of the second order Linear Extended State Observer(Linear Extended State Observer,LESO)in detail and through simulation verifies that the addition of LADRC greatly improves the low voltage ride through capability of doubly-fed generator.