Inertia Provision and Estimation of PLL-Based DFIG Wind Turbines

This paper presents an alternative inertial control method for doubly fed induction generator (DFIG)-based wind turbines by directly adjusting the phase locked loop (PLL) response. The synthetic internal voltage vector of the wind turbine-driven DFIG is defined in the electromechanical timescale to present the dynamic properties. The phase angle motion equation is further deduced to depict the relationship between the contributed inertial response and the defined internal voltage. Based on the developed motion equation, the equivalent inertia is estimated and quantified, and further found to be significantly determined by the PLL parameters. Moreover, the effect of both PLL and active power control on the defined internal voltage dynamics is also described during the inertial response. Simulated results on a modified 3-machine, 9-node test system were conducted to validate the feasibility of the proposed inertial control method and the correctness of the developed inertial characteristics.