Abstract:
The existing controls of wind turbines (WT) achieve damping provision mainly by active power modulation, which may affect the wind energy harvest. This paper proposes a two-stage control of the grid-forming direct-driven WTs to actively provide damping supports by fully using the WT resources. In stage one, two damping controllers are designed by the reactive power modulation based on the DC voltage synchronization control. The impacts of the control parameters and the operating conditions on the system stability are evaluated. The proposed controllers utilize the reactive power modulation and the DC capacitor energy for its damping provision, while the WT is operated at the maximum power point tracking (MPPT) mode. In the second stage, when the DC voltage fluctuation exceeds the designed threshold, the WT power controller immediately starts, further enhancing the system damping using the WT-side resources. An MPPT recovery process is further designed to eliminate the droop effects induced by the damper. The proposed controller does not require a frequency estimator and the active power modulation for the synchronization purposes between WT and the weak AC grid. Meanwhile, it well resolves the paradox between energy efficiency and providing strong damping support by considering the energy costs.