Transient Characteristics Analysis And Transient Overvoltage Suppression Of Wind Turbines Considering Phase Angle Jump

In recent years,with the increasing installed capacity of wind power,the impact of wind turbines on the power grid cannot be ignored.The problem of low-voltage ridethrough(LVRT)under grid short-circuit fault has always been the focus of research on wind turbines grid connection.At present,in the research on the LVRT problem of wind turbines,the influence of voltage phase angle jump on the LVRT characteristics of wind turbines is rarely considered.Accordingly,taking the mainstream doubly fed induction generator(DFIG)as the research object,this paper conducted a detailed study on the transient characteristics and the transient overvoltage problem of the DFIG during LVRT period based on the consideration of voltage phase angle jump.The main work of this article is as follows:(1)The mathematical model and the grid connection simulation model of DFIG-based wind turbines were established.Firstly,the basic structure of DFIG-based wind turbines is introduced,and the mathematical model of DFIG-based wind turbines,including wind turbines model,transmission chain model,generator model and converter model,was derived.Then,the phase-locked technology and the vector control technology of rotor side converter(RSC),grid side converter(GSC)under the synchronization rotating reference frame were analyzed.Finally,the grid connected DFIG-based wind turbines simulation model was built on the Simulink platform.(2)The DFIG transient characteristics considering phase angle jump under shortcircuit fault were analyzed.Firstly,the phase angle jump characteristics of DFIG terminal voltage were analyzed at the occurrence and clearing time of grid short-circuit fault.Then,based on the phase angle jump characteristics,the DFIG stator flux linkage,rotor back electromotive force(EMF)and rotor current analytic formulas were derived under symmetrical and asymmetric short-circuit faults,the influence of the phase angle jump on the stator flux linkage,rotor back EMF and rotor current was analyzed.Finally,Simulink was used to verify the correctness of the analysis.(3)The mechanism formation of transient overvoltage in the whole process of LVRT was studied,and a transient voltage suppression strategy was proposed.Firstly,based on the DFIG terminal voltage phase angle jump characteristics,the transient characteristics of the phase-locked loop were analyzed,and the mathematical expression of the transient voltage of the whole process of LVRT considering the phase-locked error angle was derived by combining the LVRT characteristics of DFIG.Then,according to the coupling characteristics of active/reactive current,the formation mechanism of the DFIG terminal transient voltage of was clarified,and the effects of power grid strength,phase-locked loop bandwidth,active power recovery rate and fault clearance time on the transient voltage characteristics were analyzed.Finally,a transient overvoltage suppression strategy based on phase-locked loop phase angle compensation was proposed,and Simulink was used to verify the correctness of the above analysis results and the effectiveness of the proposed control strategy.