Publication:

Single-loop droop control strategy for a grid-connected DFIG wind turbine

When grid-forming droop control strategies are implemented in grid-connected power converters, two control strategies are widely used: the single-loop and multiloop droop controls. However, only multiloop droop control strategies with inner control loops have been implemented in doubly fed induction generator (DFIG)-based wind turbines so far. This article proposes the application of a single-loop droop control strategy to a DFIG wind turbine, which has not been previously explored or implemented. As shown in the article, the application of the conventional droop control without inner control loops to DFIG-based wind power systems does not ensure a stable response. After modeling the system dynamics and evaluating its stability, two causes of instability have been identified: a resonance at the rotor electrical frequency relevant at high slips and a phase margin reduction at low slips. To solve these instability issues two control solutions are proposed: the emulation of a virtual resistor and a phase rotation. The proposed control strategy allows stabilizing the system and achieving a fast and damped dynamic response. The effectiveness of the proposed control strategy is validated by experimental results.