Effects of Active and Reactive Power Control on Inertia in DFIG-Based Wind Turbines

The inertia analysis for wind turbines (WTs) typically focuses on the electromechanical timescale. Active power control (APC) and phase-locked loop (PLL) are essential considerations while reactive power control (RPC) is often deemed negligible, particularly in stiff grid. However, such assumptions may be inappropriate. Therefore, this article aims to comprehensively examine the effects of APC and RPC on the inertia for doubly fed induction generator (DFIG)-based WTs. Firstly, phase motion models are developed by incorporating various combinations of control loops, including APC, RPC, and different PLL configurations. Subsequently, the impacts of the APC and RPC on the inertia are examined in detail. The analysis reveals that the APC diminishes inertia, whereas the RPC significantly enhances the inertia. Additionally, special attention should be given to phase characteristics of the inertia transfer function, as they can substantially influence inertial performance. Furthermore, an improved frequency support method is proposed, which achieves superior frequency response without necessitating the PLL bandwidth to be adjusted to extremely low values, such as 1 Hz or lower. Finally, the analysis and the proposed method are validated through experiments.