Enhancing Fault Ride-Through Capability of DFIG-Based WECS Using Dynamic Reconfiguration Hybrid Interlinking Transformer Technique

Abstract

The abnormal grid voltages, such as sags, swells, and harmonics caused by grid faults, seriously threaten the safe operation of a doubly-fed induction generator (DFIG)-based wind energy conversion system (WECS). To enhance the fault ride-through (FRT) capability of DFIG and improve the converter capacity utilization, this paper proposes a novel DFIG-based WECS using a dynamic reconfiguration hybrid interlinking transformer (DR-HIT) technique for performance improvement under grid faults. Multiple operating modes and flexible switching strategies were developed based on the analysis of the proposed topology and principles. The proposed DR-HIT approach smooths the DFIG ’s output power fluctuations through the cooperative control of the multifunctional converter (MFC) and grid-side converter (GSC) in shunt mode when the grid voltage is stable. Upon the occurrence of a grid voltage fault, the DR-HIT flexibly switches from shunt mode to series mode, maintaining the terminal voltage at a constant value. Additionally, once grid voltage recovers, the DR-HIT reverts flexibly to its shunt mode. Finally, simulations and experimental results demonstrate that the proposed scheme can achieve accurate control of the system and flexible switching between different modes.