This study explores tower vibrations in large-scale permanent magnet synchronous generator (PMSG)-based wind energy conversion system (WECS). First, the aerodynamic characteristics of wind turbines, including wind shear (WS), tower shadow effect (TSE), and blade airfoil structure, are examined. Then, a mechanism model of tower vibration is established, and the impacts of WS and TSE on tower vibration are analyzed. Suppression schemes, including crossing resonance zone method and tower damping control, are evaluated, and a robust variable-pitch strategy based on sliding mode control is proposed to mitigate tower vibration. Comparative analysis suggests that the proposed strategy out-performs the crossing resonance zone method and the tower damping control in achieving more effective tower vibration suppression and reducing the influence of the 3p frequency component. The effectiveness of the model and algorithm is verified through simulation experiments.