Active Power Control-Based Damping for Torsional Oscillations in Grid-Forming Type-IV Wind Turbines

Grid-forming control in Type-IV wind turbine generators can exacerbate drivetrain torsional oscillations due to rapid torque variations from DC-link voltage regulation. This paper proposes an active power control-based damping strategy that introduces damping torque indirectly via the grid-side converter, thereby avoiding direct interference with the machine-side DC-link voltage control action. A frequency-domain modeling framework is developed to guide a structured controller design procedure. In this process, the torsional mode is extracted from the rotor speed using a band-pass filter, the phase lag is compensated with a lead element, and the damping gain is determined iteratively using frequency-domain guidelines to balance damping performance and stability margins. Comparative analysis shows that the proposed method reduces the torsional oscillation envelope decay time to about 3 s, whereas existing methods exhibit slower decay and achieve over a 50% reduction in DC-link peak deviations under both phase-jump and voltage-dip scenarios. Real-time experiments on a 2$\sim ~$kW hardware setup complement the simulation studies, and an additional wind farm-level case study confirms the scalability of the approach beyond the single-machine infinite bus assumption, providing strong practical validation of the proposed damper.