To meet the requirements of improving the flexible fault ride through（FFRT） capability of double fed induction generator（DFIG） wind power system

we proposed a novel strategy of adopting three-single-phase uninterrupted dynamic voltage restorer（UDVR） with vanadium redox flow battery（VRB） energy storage. The transient characteristics of rotor side converter and grid side converter of DFIG under unbalanced grid voltage are analyzed

the charge-discharge characteristics of VRB is simulated and analyzed

and the single-phase UDVR working principle

unbalanced voltage vector and control strategy of UDVR are discussed. Furthermore

the simulation model for improving FFRT capability of DFIG wind power system based on VRB energy storage is established. The operation characteristics of DFIG-FFRT is verified by adopting the method

in which UDVR is bypass standby during grid normal operation and compensates unbalanced voltage during grid fault. The results reveal that

in view of the severe symmetrical and asymmetrical grid fault conditions

UDVR can inject compensation voltage to the grid. The DFIG wind turbine

in which green power is injected to the grid in whole voltage transient process

can improve the operation capacity of DFIG-FFRT without overshoot.