Small-Signal Stability Analysis of Weak-Grid-Connected DFIG-based WT during Asymmetric Faults

Abstract

This study develops small-signal model for doubly fed induction generator (DFIG)-based wind turbine (WT) system connected to asymmetrical-faulted weak-grid. Based on the established model, the DFIG-based WT system’s small-signal stability at the fault steady-state of weak-connection asymmetrical faults is investigated by modal analysis approach. The study shows that the DFIG-based WT system’s dynamic stability under the weak-network asymmetrical fault steady-state is dominated by phase-locked loop (PLL). Moreover, the dynamic coupling among PLL with rotor current control loop (RCCL) has an important effect on the system’s dynamic stability during asymmetrical fault steady-state. It brings negative damping effect to the system, which is not conducive to the dynamic stability. The simulation verifies the accuracy of the analysis.