The three-phase voltage source converter(VSC)is a strongly nonlinear system for a large number of power electronic switching devices and corresponding control links contained. Disturbed by the grid side fault or DC side load change in the AC/DC hybrid system

the large-capacity converter will generate complex response

which brings about unpredictable influences on the power grid. This paper studies the transient response of a three-phase VSC under typical grid fault conditions. Firstly

based on the average mode

the nonlinear characteristic of the inner current loop in the three-phase VSC is analyzed. And the Lyapunov stability criterion is adopted to analyze the stability of VSC after a grid fault. Then the fault depth and duration are taken as indices to evaluate the fault tolerance ability of VSC. Finally

the effectiveness of theoretical analysis and calculation is verified by cycle-by-cycle simulations of the grid-connected system. This work is supported by National Natural Science Foundation of China(No. 51507118)

Hubei Provincial Science and Technology Support Program(No. 2015BAA109)

and Fundamental Research Funds for the Central Universities(No. 410500078).