Transient Interaction Mechanism Analysis and Stability Control of Multi-paralleled DFIG-Based WTs during Asymmetrical Grid Faults

In this article, from the perspective of DC-link voltage (DCV) control, the transient interaction mechanism of multi-paralleled doubly fed induction generator (DFIG)-based wind turbines (WTs) is investigated during asymmetrical grid faults. Firstly, considering the coupling characteristics of positive and negative sequence (PNS) components and the interaction characteristics between the rotor side converter (RSC) and grid side converter (GSC), a large-signal nonlinear model of multiple-parallel DFIG-based WTs in DC-link voltage control time-scale is obtained. Furthermore, by using the energy function method, the dynamic interaction mechanism of multiple-parallel DFIG-based WTs is analyzed. The influence of different parameters on the transient characteristics of DC-link voltage is analyzed by using phase trajectory diagram. The dominant factors affecting the transient stability of the WTs and stability level of DC-link voltage are obtained. In addition, considering the interaction among WTs, the dynamic interaction between RSC and GSC, as well as the requirement of grid codes, a transient stability optimization strategy during asymmetrical grid faults is proposed to improve the transient stability level of the DC-link voltage and the transient stability of multiple-parallel DFIG-based WTs. Finally, simulation and experimental results validate the correctness of theoretical analysis and the effectiveness of the proposed strategy.