Study Of The Fault Features Of Doubly-fed Wind Turbines And LVRT

As the occurring of emergence problems such as energy crisis、environmentalpollution and global warming in recent years, people’s eyes have turned to thedevelopment and utilization of renewable energy. Wind power generation as a newtype sustainable utilization and green environmental protection energy, is asignificant part of the world energy strategy. As the scale of wind power is becomingmore and more big, the ratio frontal in installed capacity of power grid is increasingyear by year, causing the influence on power system increasingly highlight with theaccess of wind power. Power grid failure gives priority to the doubly-fed inductiongenerator (DFIG) which consists of the most part of wind turbines. This article ismainly aimed at the study of fault characteristics of wind turbines and the ability oflow voltage ride-through.This paper firstly analyzes the operation principle of DFIG, building themathematical modeling of DFIG under three-phase static coordinate system and dqsynchronous rotating coordinate system. The mathematical modeling and function ofthe network side converter and the rotor side converter is introduced on the basis ofDFIG mathematical modeling, and control block diagrams of network side converterand rotor side converter respectively basing on d shaft power grid voltage orientedvector control and stator flux oriented vector control.Secondly, the DFIG faults characteristics under symmetric and asymmetric faultssituations are analyzed in detail. By calculating the peak value expression of the rotorinduction electromotive force under three kinds of asymmetric faults combined withthe rotor side converter control ability, the root cause of the rotor side tilting current isrevealed. Put the maximum control voltage of rotor side converter as a constraint, wededuce the low voltage ride-through area of three asymmetric faults by the functioncurve of the slip and the peak values of rotor induced electromotive force, to measure the low voltage ride-through ability for asymmetric faults under the controlling ofrotor side voltage.Finally, the transient simulation model of DFIG wind power unit is set up inPSCAD. The paper analyzes the DFIG faults characteristics simulation undersymmetrical faults and asymmetric faults respectively and verifies the derivation oflow voltage ride-through area domains. Besides, this paper gives the capacityselecting method of STATCOM and the conclusion that: the STATCOM raises thevoltage of the terminal generator, reduces the peak values of the rotor inducedelectromotive force and improves the wind turbines’ low voltage ride-through ability.