Two-Stage Coordinated Control of Type-4 Wind Turbine with Grid-Forming Ability for Active Damping Support

Existing wind turbine (WT) control strategies realize damping support mainly by active power modulation, which may affect wind energy harvest. To improve energy efficiency and robustness, this paper proposes a two-stage coordinated control of type-4 WT for damping support using the cost-effective WT resources, where the grid-forming control is applied. In the first stage, two reactive power-based dampers are designed using DC voltage synchronization control. The impacts of the dampers on stability are analytically evaluated. In this stage, the reactive power modulation, along with the partial DC capacitor energy, are jointly utilized for damping provision, while the WT is operated at maximum power point tracking (MPPT) mode. The second stage that seeks active power modulation is only activated when the DC voltage exceeds the threshold. An MPPT recovery process is further designed to eliminate the droop errors induced by the damper. The proposed scheme is validated under various contingencies compared with existing controls. Numerical results show it does not require a frequency estimator or the active power modulation for WT synchronization and grid-forming purposes; meanwhile is relatively energy-efficient and robust to provide strong damping support.