Analysis of Subsynchronous Oscillation of Direct Drive PMSG Based Wind Farm Under Low Operating Condition

Aiming at the sub-synchronous oscillation (SSO) problem that direct-drive permanent magnetic synchronous generator (PMSG) based wind farm under low operating conditions connects to the grid, based on the idea of graphical block modeing, the wind turbine generation (WTG), collector circuit and grid are regarded as discrete components. On the basis of establishing detailed models of each component, two linearized models of direct-drive PMSG based wind farm under different collector circuit topological structure is constructed. Wind farm impedance model is constructed based on state space equation of linearized model. The influences of current inner loop control parameters, grid strength, operating conditions on SSO characteristics are analysed. The difference between the two models in the study of SSO is compared. Finally, a time-domain simulation model of direct drive PMSG based wind farm connected to grid is built in EMTDC/PSCAD and the validity of the theoretical analysis is verified.