Wind and wave loads cause structural vibrations of offshore wind turbine structures. An Active Tower Damper (ATD) system is designed to dampen these vibrations, in order to guarantee the structural integrity of these assets. However, as an undesirable consequence the newest generation of offshore wind turbines using an ATD, consisting of generator torque adaptations, are causing forced active power oscillations close to the critical EU interarea grid frequencies (0,1Hz-0,3 Hz). These oscillations can result in critical situations like grid instability, system split, and collapse. Although the current amplitude is limited, concerns are raised about their increase with the planned growth of offshore wind capacity. To ensure stable grid operation and to investigate potential mitigation actions, from an electrical and structural perspective, an in-depth study is required.