On-line Identification of Equivalent Inertia for DFIG Wind Turbines Based on Extended Kalman Filters

Abstract

This paper proposes an identification method of the equivalent inertia for doubly fed induction generator (DFIG) wind turbines. Firstly, a simplified model of DFIG incorporating phase-locked loop (PLL) and virtual inertia control is developed based on the analysis of mathematical model and control strategy of DFIG. On the basis, the equivalent motion equation of DFIG similar to the rotor motion equation of synchronous generators (SGs) is derived considering the dynamic characteristics of PLL and active power control model. According to the equivalent motion equation, the mathematical expression of equivalent inertia of DFIG wind turbines is derived. And then, an extended Kalman filter (EKF) based identification method for the controller parameters in the expression of equivalent inertial is proposed to quantitatively characterize the equivalent inertia of DFIG wind turbines. Finally, the effectiveness and accuracy of the proposed method is verified on a modified 4-machine 2-area system.