The stability of multi-terminal flexible DC systems with virtual synchronous generators(VSG)is studied. Firstly

the transfer function models of voltage source converter(VSC)controlled by VSG or vector are developed respectively. Secondly

the influence of VSG access on the stability of multi-terminal DC(MTDC)system is analyzed by the damping torque method. Then the following conclusions are drew: 1)the assumption that “the power injected into VSG from the DC side is constant” ignores the dynamic interaction between the VSG and remaining DC system

which leads its results not to be general; 2)there are stability risks in MTDC system with VSGs

and the system is affected by the control parameters of VSG and the dynamic interaction between the VSG and remaining DC system; 3)the oscillations may happen in the MTDC system when the open-loop mode of VSG is close to the open-loop mode of the remaining DC system

thus this paper proposes an effective parameter adjustment method. Finally

the time-domain simulation analysis of a three-terminal flexible DC system with VSGs is carried out and the above results are verified.