In the wind-thermal bundling AC/DC hybrid system transmission mode

if AC line exit operation

itsmode of operation will change as the pure DC delivery

if not timely switching control strategy

there will be a largenumber of surplus power

and lead to a continuous rise in the system frequency and voltage amplitude

at the sametime

the power angle also loses stability and affects the operation of the system. To solve the problem

firstly analyz-es the AC/DC operation and pure DC operation of two different operation mode control strategy

and then accordingto the changes of the electric parameters of the fault

this paper puts forward a operation mode switch control strate-gy

and building model in the simulation platform. Studies show that the strategy can rapid detection to phase offsetand timely detection of frequency change taking the opportunity according to the switch control strategy. At the sametime after switching to maintain the stability of the system frequency and AC system voltage. Finally

when the ACline fault is cleared

electric parameters restore to the original level

will transform operation mode for AC/DC opera-tion of the original.