The grid-side converter for offshore wind power primarily adopts grid-following type. The interaction between weak AC grid and offshore wind turbines at the control time scale leads to wide-band oscillations. In order to analyze the dynamic stability and oscillation characteristics of the source grid under the new electricity system

the parameters of offshore wind power were taken as reference

and the unified amplitude-phase motion model for offshore wind power was established. The modal analysis was used to solve for weak damping mode and participation factors. The impact of the torsional vibration frequency under weak AC grid on the damping characteristics of offshore wind power was solved. The influences of the length of submarine cables and the bandwidth of PLL on the dynamic stability of the source-grid system were analyzed. Moreover

the differences in source-grid damping characteristics under various capacities of offshore wind power were calculated

and the impact of wind farm operating power and control strategies on system operating characteristics was revealed. The results indicate that weak AC system is the primary factor which causes weak damping. However

the selection of the PLL bandwidth is key to improving the oscillation characteristics. Offshore wind power under active power control exhibits weak damping. In weak AC grid

the interaction between source and grid is enhanced. The analysis results provide reliable references for the safe and stable operation of the power grid.