Reduced-order modeling of DFIG-based wind turbine connected into weak AC grid based on electromechanical time scale

Abstract

Nowadays, the stability issue of the doubly fed induction generator (DFIG)-based wind turbines tied into weak AC power grid has attracted more and more attention. To analyze the stability of such cascade system, it is a common way to establish the small-signal model of the whole system. Although there have been various modeling methods, few of them can be easily utilized in practice due to the high order of the presented models. To address this issue, this paper simplifies the fast time scale subsystems and proposes a reduced-order state space model of the DFIG system based on electromechanical time scale, considering the rotor current controller (RCC), the phase-locked loop (PLL), the remained value of the grid voltage, and the impedance of the weak AC grid as well. Based on the simplified model, the stability of the wind turbine during weak AC grid voltage dips can be easily analyzed. The correctness of the integrated model and its convenience for stability analysis have been proved by eigenvalue matching method and computer simulations.

Keywords

• Doubly fed induction generator (DFIG)
• Wind turbine
• Phase-locked loop (PLL)
• Weak AC grid
• Electromechanical time scale