For the frequent sub-synchronous oscillation（SSO）phenomena in the grid connection from the transmission end of direct drive permanent magnet wind turbine generators（D-PMSGs）based wind farms in direct-current vicinity of Hami area

in this paper

the equivalent model of wind power interconnection including multiple direct drive permanent magnet wind turbine generators（D-PMSGs）is set up

the equivalent model and mechanism of the D-PMSGs to the sub-synchronous oscillation are studied.Then

the issue of sub synchronous oscillation due to interaction of both D-PMSGs and weak AC system is studied by the use of eigenvalue analysis method.After that

the influence of such factors as system impedance

wind power output

number and control parameters of D-PMSGs etc.

on the feature of wind power sub synchronous oscillation is simulated and analyzed.It is shown by the simulation result that in case of interconnection of the D-PMSGs by the weak transmission line

its ineraction with the weak AC system generates a pair of characteristic root with weak impedance

of which the real part is positive

showing that sub-synchronous oscillation mode is instable.Multiple influence factors have different effects on the SSO characteristics of wind farm.Finally

the suppression effect of SVG additional damping control on sub-synchronous harmonic is preliminarily verified by real time digital simulation experiment.